Low stress relaxation elastomeric materials

ABSTRACT

A low stress relaxation elastomeric material comprises a block copolymer having an elasotmeric soft block portion and thermoplastic hard block portions, at least one vinylarene resin and mineral oil. The elasotmeric material may be used in a film comprising an elastomeric layer and at least one substantially less elastomeric skin layer. The skin layer comprises a thermoplastic polymer such as polyolefins. The film exhibits desired elastic and stress relaxation properties at body temperature. The film is useful in forming a macroscopically-expanded, three-dimensional elastomeric web.

This application is a continuation of Ser. No. 09/398,849, filed Sep.17, 1999, now abandoned.

FIELD OF THE INVENTION

The present invention relates to low stress relaxation elastomericmaterials suitable for use in macroscopically-expanded,three-dimensional, apertured polymeric webs.

BACKGROUND OF THE INVENTION

It has long been known in the field of disposable absorbent articlesthat it is desirable to construct absorptive devices, such as disposablediapers with fasteners, pull-on diapers, training pants, sanitarynapkins, pantiliners, incontinent briefs, and the like, with elasticelements to improve the range of size, ease of motion, and sustainedfit. It is also well known that it is preferable, especially in suchproducts intended to be worn in hot and humid conditions, to provideadequate porosity to all areas of the article where undue occlusion ofthe skin may cause sensitized skin or heat rash. Due to the nature ofmany disposable absorbent articles there is a high potential for skinirritation due to trapping of moisture and other body exudates betweenthe elasticized portion of the article and the skin of the wearer.Elasticized portions of disposable articles are particularly prone tocausing skin irritations as they tend to be more conformable to thebody, and therefore more likely to occlude areas of the skin, often forlong periods of time. Various methods are known in the art for impartingelasticity to polymer films. As materials with greater elasticityprovide health care or personal hygiene products with a better fit tothe body, the air flow to the skin and the vapor flow from the occludedareas are reduced. Breathability (particularly vapor permeability)becomes more important for skin health. Various methods are also knownin the art for imparting porosity to polymer films to improvebreathability, but there remains a need for a polymeric film or web thatprovides for both adequate elasticity and porosity, such as may beadapted for durable, prolonged use in personal hygiene or health careproducts, particularly disposable articles, bandages, wraps, and wounddressings.

Disposable diapers and other absorbent articles fitted with elasticizedleg cuffs or elasticized waist bands for a more comfortable fit, as wellas providing for better leakage control, are known in the art. Often,the elasticity is accomplished with a heat treatment of polymericmaterials that results in a desirable shirring or gathering of a portionof the diaper. One such method of treatment is disclosed in U.S. Pat.No. 4,681,580, issued to Reising et al. on Jul. 21, 1987, and herebyincorporated by reference herein. Other methods for imparting elasticityare taught in U.S. Pat. No. 5,143,679 issued to Weber et al. on Sep. 1,1992, U.S. Pat. No. 5,156,793 issued to Buell et al. on Oct. 20, 1992and U.S. Pat. No. 5,167,897 issued to Weber et al. on Dec. 1, 1992, allare hereby incorporated by reference herein.

Several means of rendering elasticized planar polymer films more porousare known in the art, such as die punching, slitting, and hot-pin meltaperturing. However, when any of the above techniques is applied tothermoplastic elastomeric films, the increase in porosity is accompaniedby a decrease in the degree of reliable elastic performance. Forexample, in the case of circular apertures in a planar film, it is wellknown that for an applied stress S₁, a resultant local stress, S₂, iscreated orthogonal to the applied stress about the apertures. This localstress, S₂, is greater than S₁, approaching a magnitude up to 3 timesthe applied stress. For non-round apertures the concentration of stresscan be even greater. As a result, apertures become sources of tearinitiation sites at their edges, because the edges of the material formthe edges of the apertures in the plane of applied stress. For commonthermoplastic elastic films, such apertures facilitate tear initiationwhich can propagate over time leading to catastrophic failure of thefilm. When used in elasticized portions of disposable absorbentarticles, this failure results in the loss of important elasticcharacteristics, including loss of comfort, fit and use of the absorbentarticle.

Prior art web structures that do provide adequate porosity so as to bepreferable for use as the wearer-contacting surface on disposableabsorbent articles have been of two basic varieties, i.e., inherentlyfluid-pervious structures, such as fibrous nonwovens, andfluid-impervious materials such as polymeric webs which have beenprovided with a degree of fluid permeability via aperturing to permitfluid and moisture flow therethrough. Neither variety ischaracteristically elastic, and as a result both are generally used inregions of an absorbent article requiring fluid permeability but notextensibility, such as the body-contacting layer of a catamenial pad.

Commonly assigned U.S. Pat. No. 3,929,135 issued to Thompson on Dec. 30,1975, and hereby incorporated herein by reference, suggests a suitablebody-contacting porous polymeric web for disposable articles. Thompsonteaches a macroscopically-expanded, three-dimensional topsheet comprisedof liquid-impermeable polymeric material. However, the polymericmaterial is formed to comprise tapered capillaries, the capillarieshaving a base opening in the plane of the topsheet, and an apex openingin intimate contact with the absorbent pad utilized in the disposableabsorbent article. The polymer material taught by Thompson is notgenerally an elastomer, however, and Thompson depends on the inelasticproperties of the heat-molded single layer film to produce the desiredthree-dimensional structure.

Still another material which has been utilized as a body contactingsurface in a disposable absorbent article context is disclosed incommonly assigned U.S. Pat. No. 4,342,314 issued to Radel et al. on Aug.3, 1982, and hereby incorporated herein by reference. The Radel et al.patent discloses an improved macroscopically-expanded three-dimensionalplastic web comprising a regulated continuum of capillary networksoriginating in and extending from one surface of the web and terminatingin the form of apertures in the opposite surface thereof. In a preferredembodiment, the capillary networks are of decreasing size in thedirection of liquid transport.

The macroscopically-expanded three-dimensional plastic webs of the typegenerally described in the aforementioned commonly assigned Thompson andRadel et al. patents have met with good success in permitting adequatevapor permeability due to the porosity provided by the apertreg.However, because of material limitations such webs do not generallypossess the requisite elasticity to allow the resulting web to havesignificant elastomeric characteristics. This shortcoming substantiallylimits the use of such webs in elasticized portions of an absorbentarticle.

Elasticized polymeric webs may be produced from elastomeric materialsknown in the art, and may be laminates of polymeric materials such asdisclosed in U.S. Pat. No. 5,501,679, issued to Krueger et al. on Mar.26, 1996. Laminates of this type are generally prepared by coextrusionof elastomeric materials and inelastic skin layers followed bystretching the laminate past the elastic limit of the skin layers andthen allowing the laminate to recover. Elastomeric webs or films such asthose described above may be used in the body hugging portions ofgarments, such as the waistbands, leg cuffs and side panels, but aregenerally not porous enough to prevent undesirable skin irritations whenused for prolonged periods of time.

Additionally, the actual use condition for absorbent articles or otherpersonal care products typically involves heat, humidity, loading orcombinations thereof. Some elastomeric materials suffer loss of elasticproperties and dimensional stability at body temperature, especiallyunder load or tension. The loss of elastic properties and dimensionalstability results in sagging and ill-fitting of the absorbent article,and in severe cases, leakage from the absorbent article may result.

The elastic components of certain articles, such as training pants,pull-on diapers, disposable diapers with fasteners, adult incontinencegarments, bandages, wraps, wound dressings, and the like, may besubjected to considerable amount of stretching, at a strain as large as400% of its original dimension, while the article is being put on thebody of the wearer. This step imposes additional requirements ofstretchability and recoverability on the elastomeric material.

There is considerable difficulty in processing and handling elastomericmaterials, due to the inherent tacky and stretchy nature of theelastomeric materials. The elastomeric materials have a tendency tostick to the processing equipment, and are difficult to remove from aroll or cut to the correct size to be incorporated into the finishedproducts.

Therefore, it is desirable to provide an elastomeric material whichsubstantially retain its elastic properties under actual use conditionof the finished product over a specified period of time, for example, atbody temperature under sustained load for about 10 hours.

It is desirable to provide such an elastomeric film that is form-fittingand breathable (i.e., vapor permeable).

More particularly, in a particularly preferred embodiment, it would bedesirable to provide a macroscopically-expanded three-dimensionalapertured elastomeric web that is able to substantially recover itsthree-dimensional shape after being subjected to an applied strain of upto about 400% or more.

It is further desirable to provide an elastomeric film suitable for usein an apertured elastomeric web designed to dissociate the effects of anapplied strain on the web from the edges of the apertures and henceretard or prevent the onset of tear initiation.

Furthermore, it is desirable to provide such an elastomeric materialthat has improved processability and is cost-effective for personalhygiene products and health care products, such as pull-on diapers,training pants, disposable diapers with fasteners, incontinencegarments, sanitary napkins, pantiliners, wound dressings, bandages, andwraps.

SUMMARY OF THE INVENTION

The present invention pertains to a low stress relaxation elastomericmaterial. The elastomeric material can be used alone or with skin layersto form an elastomeric film. The elastomeric film is useful in a formingprocess to provide a porous, macroscopically-expanded,three-dimensional, elastomeric web. In a preferred embodiment, theelastomeric web is suitable for use in elasticized or body-huggingportions of disposable absorbent articles such as side panels, waistbands, cuffs, or of health care products such as dressings, bandages andwraps. The porous extensible polymeric webs of the present invention mayalso be used in other portions of the absorbent articles where astretchable or breathable material is desired, such as topsheets orbacksheets.

The elastomeric materials of the present invention preferably exhibitlow stress relaxation at body temperature and under load or stress for aspecified period of time. The elastomeric materials also exhibit lowhysteresis and high elongation at break when subjected to a largedeformation. In a preferred embodiment, the elastomeric materialcomprises a styrenic block copolymer such aspolystyrene-poly(ethylene/propylene)-polystyrene (S-EP-S),polystyrene-poly(ethylene/butylene)-polystyrene (S-EB-S),polystyrene-polybutylene-polystyrene (S-B-S),polystyrene-polyisoprene-polystyrene (S-I-S), or hydrogenatedpolystyrene-poly(isoprene/butadiene)-polystyrene (S-IB-S) at least onevinylarene resin, and a processing oil, particularly a low viscosityhydrocarbon oil such as mineral oil.

The elastomeric materials of the present invention may be in amonolithic film or in a multilayer film with at least one substantiallyless elastomeric skin layer such as polyolefin type materials, includingpolyethylene and polypropylene. The elastomeric films are useful informing macroscopically-expanded, three dimensional, elastomeric webs.

In a preferred embodiment, the web has a continuous first surface and adiscontinuous second surface remote from the first surface. Theelastomeric web exhibits a multiplicity of primary apertures in thefirst surface of the web, the primary apertures being defined in theplane of the first surface by a continuous network of interconnectingmembers, each interconnecting member exhibiting an upwardlyconcave-shaped cross-section along its length. In a preferred embodimenteach interconnecting member exhibits a generally U-shaped cross-sectionalong a portion of its length, the cross-section comprising a baseportion generally in the plane of the first surface of the web andsidewall portions joined to each edge of the base portion andinterconnected with other sidewall portions. The interconnected sidewallportions extend generally in the direction of the second surface of theweb, and are interconnected to one another intermediate the first andthe second surfaces of the web. The interconnected sidewall portionsterminate substantially concurrently with one another to form asecondary aperture in the plane of the second surface of the web.

When used as an extensible, porous member in an absorbent article, theelastomeric layer of the present invention allows the interconnectingmembers to stretch in the plane of the first surface. Thethree-dimensional nature of the web allows the strain on theinterconnecting members in the plane of the first surface to bedissociated from the strain at the secondary apertures in the secondarysurface, and therefore decoupled from potential strain-induced stress attear initiation sites. This dissociation, or decoupling, of thestrain-induced stress of the web from strain-induced stress at thesecondary apertures significantly increases web reliability by allowingrepeated and sustained web strains of up to about 400% or more withoutfailure of the web due to tear initiation at the apertures.

Also disclosed is a method of producing the elastomeric web of thepresent invention which comprises providing a multilayer elastomericfilm, supporting the film on a forming structure, and applying a fluidpressure differential across the thickness of the multilayer film. Thefluid pressure differential is sufficiently great to cause themultilayer film to conform to the supporting structure and rupture in atleast portions of the formed film.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of the present invention, itis believed that the present invention will be better understood fromthe following description taken in conjunction with the accompanyingdrawings in which like reference numerals identify identical elementsand wherein:

FIG. 1 is an enlarged, partially segmented, perspective illustration ofa prior art polymeric web of a type generally disclosed in commonlyassigned U.S. Pat. No. 4,342,314;

FIG. 2 is an enlarged, partially segmented, perspective illustration ofa preferred elastomeric web of the present invention having two layersof polymer film, at least one of which is elastomeric;

FIG. 3 is a further enlarged, partial view of a web of the typegenerally shown in FIG. 2, but illustrating in greater detail the webconstruction of an alternative elastomeric web of the present invention;

FIG. 4 is an enlarged cross-sectional view of a preferred multilayerfilm of an elastomeric web of the present invention having anelastomeric layer interposed between two skin layers;

FIG. 5 is a plan view of aperture shapes projected in the plane of thefirst surface of an alternative elastomeric web of the presentinvention;

FIG. 6 is an enlarged cross-sectional view of an interconnecting membertaken along section line 6—6 of FIG. 5;

FIG. 7 is another enlarged cross-sectional view of an interconnectingmember taken along section line 7—7 of FIG. 5;

FIGS. 8A-8C are schematic representations of a cross-section of anaperture of an elastomeric web of the present invention in variousstates of tension;

FIG. 9 is an enlarged optical photomicrograph showing the first surfaceof an elastomeric web of the present invention having an ordered patternof approximately 1 mm square apertures;

FIG. 10 is an enlarged scanning electron microscope photomicrographperspective illustration of the second surface of the elastomeric webshown in FIG. 9 in an unstretched state;

FIG. 11 is an enlarged scanning electron microscope photomicrographperspective illustration of the second surface of the elastomeric webshown in FIG. 9 tensioned to approximately 100% elongation;

FIG. 12 is an enlarged scanning electron microscope photomicrographperspective illustration of an aperture of an elastomeric web of thepresent invention showing rugosities formed after extension andrecovery;

FIG. 13 is a partially segmented perspective illustration of adisposable garment comprising the elastomeric web of the presentinvention;

FIG. 14 is a simplified, partially segmented illustration of a preferredembodiment of side panels for a disposable garment;

FIG. 15 is a simplified, partially exploded perspective illustration ofa laminate structure generally useful for forming the web structureillustrated in FIG. 2;

FIG. 16 is a perspective view of a tubular member formed by rolling aplanar laminate structure of the type generally illustrated in FIG. 15to the desired radius of curvature and joining the free ends thereof toone another;

FIG. 17 is a simplified schematic illustration of a preferred method andapparatus for debossing and perforating an elastomeric film generally inaccordance with the present invention;

FIG. 18 is an enlarged, partially segmented perspective illustration ofan alternative elastomeric web of the present invention; and

FIG. 19 is an enlarged cross sectional illustration of the web of FIG.18 taken along section line 19—19.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

As used herein, the term “comprising” means that the various components,ingredient, or steps can be conjointly employed in practicing thepresent invention. Accordingly, the term “comprising” encompasses themore restrictive terms “consisting of” and “consisting essentially of”.

As used herein, the terms “elastic” or “elastomeric” refer to anymaterial which is capable of being elongated or deformed under anexternally applied force, and which will substantially resume itsoriginal dimension or shape, sustaining only small permanent set(typically no more than about 20%), after the external force isreleased. The term “elastomer” refers to any material exhibiting elasticproperties as described hereinabove.

As used herein, the term “thermoplastic” refers to any material whichcan be melted and resolidified with little or no change in physicalproperties (assuming a minimum of oxidative degradation).

As used herein the term “skin layer” refers to a layer comprising athermoplastic polymer or polymeric blend that is substantially lesselastomeric than the elastomeric layer. The skin layer is considered“substantially less elastomeric” if the permanent set of the skin layeris at least about 20% greater than that of the elastomeric layer.Permanent set refers to the deformation of a material measured in asufficient time after the material is released from a specifiedelongation to allow the material to snap back fully.

As used herein, the term “percent elongation” refers to the differencebetween the length of an elastomeric material measured while thematerial is elongated under an applied force and the length of thematerial in its undeformed or unstrained state, dividing by the lengthof the material in its undeformed state, then multiplying by 100. Forexample, a material in its undeformed or unstrained state has a 0%elongation.

As used herein, the terms “set” or “percent set” refer to the percentdeformation of an elastomeric material measured while the material is ina relaxed condition for a specified period of time (i.e., 60 seconds forthe Test Methods described herein) after the material was released froma specified elongation without allowing the material to snap backcompletely. The percent set is expressed as [(zero load extension afterone cycle—initial sample gauge length of cycle 1)/(initial sample gaugelength of cycle 1)]×100. Zero load extension refers to the distancebetween the jaws at the beginning of the second cycle before a load isregistered by the tensile testing equipment.

As used herein, the term “stress relaxation” refers to the percentageloss of tension or load between the maximum load or force encounteredafter elongating an elastomeric material at a specific rate of extensionto a predetermined length (or the load or force measured at some initiallength) and the remaining load or force measured after the sample hasbeen held at that length or elongation for a specified period of time.Relaxation is expressed as percentage loss of the initial loadencountered at a specific extension of an elastomeric material.

As used herein, the term “hysteresis” refers to the difference betweenthe energy retained by an elastomeric material during retraction from aspecified elongation and the energy required to subsequently elongatethe elastomeric material to that previous length. Stretching anelastomeric material to a specified elongation, typically 200%elongation, and returning to zero load completes a hysteresis loop.

Other terms are defined herein where initially discussed.

FIG. 1 is an enlarged, partially segmented, perspective illustration ofa prior art macroscopically-expanded, three-dimensional, fiber-like,fluid pervious polymeric web 40 which has been found highly suitable foruse as a topsheet in disposable absorbent articles, such as diapers andsanitary napkins. The prior art web is generally in accordance with theteachings of commonly assigned U.S. Pat. No. 4,342,314 issued to Radelet al. on Aug. 3, 1982, which is hereby incorporated herein byreference. The fluid pervious web 40 exhibits a multiplicity ofapertures, e.g., apertures 41, which are formed by a multiplicity ofinterconnected fiber-like elements, e.g., fiber-like elements 42, 43,44, 45, and 46 interconnected to one another in the first surface 50 ofthe web. Each fiber-like element comprises a base portion, e.g., baseportion 51, located in plane 52 of the first surface 50. Each baseportion has a sidewall portion, e.g., sidewall portion 53, attached toeach edge thereof. The sidewall portions extend generally in thedirection of the second surface 55 of the web. The intersecting sidewallportions of the fiber-like elements are interconnected to one anotherintermediate the first and second surfaces of the web, and terminatesubstantially concurrently with one another in the plane 56 of thesecond surface 55.

In a preferred embodiment, the base portion 51 includes a microscopicpattern of surface aberrations 58 generally in accordance with theteachings of U.S. Pat. No. 4,463,045, issued to Ahr et al. on Jul. 31,1984, the disclosure of which is hereby incorporated herein byreference. The microscopic pattern of surface aberrations 58 provides asubstantially non-glossy visible surface when the web is struck byincident light rays.

In an alternative embodiment the prior web may include a multiplicity ofmuch smaller capillary networks (not shown) in the first surface 50 ofthe web, as taught by U.S. Pat. No. 4,637,819 to Ouellette et al. issuedJan. 20, 1987 and hereby incorporated herein by reference. It isbelieved that the additional porosity afforded by the smallerfluid-handling capillary networks may allow the web of the presentinvention function more efficiently when used as an extensible, porousportion of a disposable absorbent article.

As utilized herein, the term “interconnecting members” refers to some orall of the elements of the elastomeric web, portions of which serve todefine the primary apertures by a continuous network. Representativeinterconnecting members include, but are not limited to, the fiber-likeelements of the aforementioned '314 Radel et al. patent and commonlyassigned U.S. Pat. No. 5,514,105 to Goodman, Jr., et al. issued on May7, 1996 and hereby incorporated herein by reference. As can beappreciated from the following description and drawings, theinterconnecting elements are inherently continuous, with contiguousinterconnecting elements blending into one another in mutually-adjoiningtransition portions.

Individual interconnecting members can best be generally described, withreference to FIG. 1, as those portions of the elastomeric web disposedbetween any two adjacent primary apertures, originating in the firstsurface 50 and extending to the second surface 55. On the first surfaceof the web the interconnecting members collectively form a continuousnetwork, or pattern, the continuous network of interconnecting membersdefining the primary apertures, and on the second surface of the web theinterconnecting sidewalls of the interconnecting members collectivelyform a discontinuous pattern of secondary apertures.

As utilized herein, the term “continuous”, when used to describe thefirst surface of the elastomeric web, refers to the uninterruptedcharacter of the first surface, generally in the plane of the firstsurface. Thus, any point on the first surface can be reached from anyand every other point on the first surface without substantially leavingthe first surface in the plane of the first surface. Likewise, asutilized herein, the term “discontinuous,” when used to describe thesecond surface of the elastomeric web, refers to the interruptedcharacter of the second surface, generally in the plane of the secondsurface. Thus, any point on the second surface cannot be reached fromevery other point on the second surface without substantially leavingthe second surface in the plane of the second surface.

In general, as utilized herein the term “macroscopic” is used to referto structural features or elements which are readily visible to a normalhuman eye when the perpendicular distance between the viewer's eye andthe plane of the web is about 12 inches. Conversely, the term“microscopic” is utilized to refer to structural features or elementswhich are not readily visible to a normal human eye when theperpendicular distance between the viewers eye and the plane of the webis about 12 inches.

As utilized herein, the term “macroscopically-expanded”, when used todescribe three-dimensional elastomeric webs, ribbons and films, refersto elastomeric webs, ribbons and films which have been caused to conformto the surface of a three-dimensional forming structure so that bothsurfaces thereof exhibit the three-dimensional pattern of the formingstructure. Such macroscopically-expanded webs, ribbons and films aretypically caused to conform to the surface of the forming structures byembossing (i.e., when the forming structure exhibits a pattern comprisedprimarily of male projections), by debossing (i.e., when the formingstructure exhibits a pattern comprised primarily of female capillarynetworks), or by extrusion of a resinous melt onto the surface of aforming structure of either type.

By way of contrast, the term “planar” when utilized herein to describeplastic webs, ribbons and films, refers to the overall general conditionof the web, ribbon or film when viewed by the naked eye on a macroscopicscale. For example, a non-apertured extruded film or an aperturedextruded film that does not exhibit significant macroscopic deformationout of the plane of the film would generally be described as planar.Thus, for an apertured, planar web the edge of the material at theapertures is substantially in the plane of the web, causing applied webstresses in the plane of the web to be coupled directly to tearinitiation sites at the apertures.

When macroscopically-expanded, the multilayer film of the elastomericweb of the present invention is formed into three-dimensionalinterconnecting members which may be described as channel-like. Theirtwo-dimensional cross-section may also be described as “U-shaped”, as inthe aforementioned Radel et al. patent, or more generally as “upwardlyconcave-shaped”, as disclosed in the aforementioned Goodman, Jr., et al.patent. “Upwardly concave-shaped” as used herein describes theorientation of the channel-like shape with relation to the surfaces ofthe elastomeric web, with the base generally in the first surface, andthe legs of the channel extending from the base in the direction of thesecond surface, and with the channel opening being substantially in thesecond surface. In general, as described below with reference to FIG. 5,for a plane extending through the web orthogonal to the plane of thefirst surface and intersecting any two adjacent primary apertures, theresulting cross-section of an interconnecting member disposed betweenwill exhibit a generally upwardly concave shape that may besubstantially U-shaped.

Several means of rendering non-apertured planar elasticized polymericwebs more porous are known in the art, such as die punching, slitting,and hot-pin melt aperturing. However, when any of the above techniquesis applied to thermoplastic elastomeric films, the increase in porosityis typically accompanied by a decrease in the degree of reliable elasticperformance. Once perforated by conventional methods the edges of theapertures become sources of tear initiation sites as forces are appliedto the web since they lie in the plane of applied stress. For commonthermoplastic elastic films, web stress will initiate tears at theapertures which propagate over time leading to catastrophic failure ofthe film. If the aperture shapes are non-round, e.g., square,triangular, or other polygons, potential for tear initiation increasesdue to the stress concentrations at the angular intersection of sides.

Applicant has found in the present invention that by utilizing amultilayer polymeric web comprising an elastomeric layer in combinationwith at least one skin layer, and forming the multilayer web into amacroscopically-expanded, three-dimensional configuration according tothe method described herein, the resulting elastomeric web exhibits theadvantages of high porosity and high elasticity, as well as reliability,and high strength.

Preferably, the elastomeric layer itself is capable of undergoing from50% to 1200% elongation at room temperature when in a non-apertured,planar condition. The elastomer can be either pure elastomers or a blendwith an elastomeric phase or content that will still exhibit substantialelastomeric properties at ambient temperatures, including human bodytemperatures. The elastomeric materials of the present invention, mayexhibit desired elastic and stress relaxation properties, in amonolithic film, in a multilayer film with at least one elastomericlayer, or in a porous, three-dimensional web made according to themethod described herein. Preferably the elastomeric materials of theexhibit a stress relaxation at 200% elongation of less than about 20%,more preferably less than about 30%, and most preferably less than about40% at room temperature. The elastomeric materials of the presentinvention exhibits a stress of less than about 45%, preferably less thanabout 50%, and more preferably less than about 55% relaxation, at 50%elongation after 10 hours at body temperature (about 100° F.).

The skin layer of the present invention is preferably thinner andsubstantially less elastic than the elastomeric layer, and may in thelimiting case be generally inelastic. There may be more than one skinlayer used in conjunction with the elastomeric layer of the presentinvention, and it, or they, will generally modify the elastic propertiesof the elastomer. If more than one skin layer is used, the skin layersmay have the same or different material characteristics.

FIG. 2 is an enlarged partially segmented, perspective illustration of amacroscopically-expanded, three-dimensional, elastomeric web embodimentof the present invention, generally indicated as 80. The geometricalconfiguration of the fluid-pervious, elastomeric web 80 is generallysimilar to that of prior art web 40, illustrated in FIG. 1, and isgenerally in accordance with the teachings of the aforementioned '314Radel et al. patent. Other suitable formed film configurations aredescribed in U.S. Pat. No. 3,929,135, issued to Thompson on Dec. 30,1975; U.S. Pat. No. 4,324,246 issued to Mullane, et al. on Apr. 13,1982; and U.S. Pat. No. 5,006,394 issued to Baird on Apr. 9, 1991. Thedisclosures of each of these patents are hereby incorporated herein byreference.

A preferred embodiment of an elastomeric web 80 of the present inventionexhibits a multiplicity of primary apertures, e.g., primary apertures71, which are formed in plane 102 of the first surface 90 by acontinuous network of interconnecting members, e.g., members 91, 92, 93,94, 95 interconnected to one another. The shape. of primary apertures 71as projected on the plane of the first surface 90 are preferably in theshape of polygons, e.g., squares, hexagons, etc., in an ordered orrandom pattern. In a preferred embodiment each interconnecting membercomprises a base portion, e.g., base portion 81, located in plane 102,and each base portion has a sidewall portion, e.g., sidewall portions83, attached to each edge thereof. The sidewall portions 83 extendgenerally in the direction of the second surface 85 of the web andintersect with side walls of adjoining interconnecting members. Theintersecting sidewall portions are interconnected to one anotherintermediate the first and second surfaces of the web, and terminatesubstantially concurrently with one another to form a secondaryaperture, e.g., secondary apertures 72 in the plane 106 of the secondsurface 85. Detailed description of the porous macroscopically-expanded,three-dimensional elastomeric web is disclosed in U.S. patentapplication Ser. No. 08/816,106, now abandoned filed on Mar. 14, 1997 byCurro et al., the disclosure of which is incorporated herein byreference.

FIG. 3 is a further enlarged, partial view of a web of the typegenerally similar to web 80 of FIG. 2, but illustrating an alternativeweb construction according to the present invention. The multilayerpolymeric formed film 120 of web 80 is preferably comprised of at leastone elastomeric layer 101, and at least one skin layer 103. While FIG. 3shows a two-layer embodiment with the skin layer 103 nearer the firstsurface 90, it is believed that the order of layering of the formed film120 is not limiting. While it is presently preferred that as shown inFIG. 3 the polymeric layers terminate substantially concurrently in theplane of the second surface, it is not presently believed to beessential that they do so, i.e., one or more layers may extend furthertoward the second surface than the others. The elastomeric layercomprises from about 20% to about 95% of the total thickness of the filmand each skin layer comprises from about 1% to about 40% of the totalthickness of the film. Typically, the elastomeric film has a thicknessof from about 0.5 mils to about 20 mils, preferably from about 1.0 milto 5.0 mils. Each skin layer is typically about 0.05 mil to about 5 milsthick, and preferably from about 0.1 mil to about 1.5 mils thick. In apreferred embodiment, the elastomeric layer is about 3.2 mils thick andeach skin layer is about 0.15 mil thick.

A particularly preferred multilayer polymeric film 120 of the web 80 isdepicted in cross-section in FIG. 4, showing an elastomeric layer 101interposed between two skin layers 103. The elastomeric layer 101preferably comprises a thermoplastic elastomer having at least oneelastomeric portion and at least one thermoplastic portion. Thethermoplastic elastomer typically comprises a substantially continuousamorphous matrix, with glassy or crystalline domains interspersedthroughout. Not intending to be bound by theory, it is believed that thediscontinuous domains act as effective physical crosslinks which enablethe material to exhibit an elastic memory when the material is subjectedto an applied strain and subsequently released. Preferred thermoplasticelastomeric materials include block copolymers and blends thereof. Thethermoplastic elastomeric materials suitable for use in the presentinvention include styrene-butadiene-styrene or like styrenic blockcopolymers. Also suitable for use herein as the thermoplasticelastomeric materials are certain polyolefins which exhibit the desiredthermoplastic elastomeric character and resultant elastic properties,for example, polyethylenes and polypropylenes having densities belowabout 0.90 g/cc. The skin layers preferably comprise substantially lesselastomeric materials such as polyolefins having densities greater thanabout 0.90 g/cc or other thermoplastic materials. The skin layers shouldhave sufficient adhesion to the elastomeric layer such that it will notcompletely delaminate either before or after stretching of the web. Thematerials suitable for use herein as the skin layer should have thedesired melt flow properties such that it can be successfully processedwith the elastomeric layer to form a multilayer film. A preferred methodto produce the multilayer polymeric film 120 is coextrusion.

In general, an elastomeric, low stress relaxation material with desiredelastic and stress relaxation properties may be prepared from acomposition which comprises an elastomeric block copolymer, at least onethermoplastic resin or blend and a low viscosity processing oil. Apreferred composition comprises about 55 wt % of a styrenic-olefinictriblock copolymer, about 15 wt % of polystyrene, and about 30 wt % ofmineral oil. The compositions may further include other additives suchas antioxidants, anti-block agents and anti-slip agents. Typically theantioxidants are no more than 1%, preferably no more than 0.5% of thetotal weight of the elastomeric compositions.

A number of block copolymers can be used to prepare the elastomericcompositions useful in preparing the low stress relaxation clastomericfilm or sheet of the present invention. Linear block copolymers, such asA-B-A triblock copolymers, A-B-A-B tetrablock copolymers, A-B-A-B-Apentablock copolymers, or the like, are suitably selected on the basisof block content and average molecular weights of the blocks. Such blockcopolymers generally comprise an elastomeric block portion B and athermoplastic block portion A. The block copolymers suitable for useherein are thermoplastic and elastomeric. The block copolymers areelastomeric in the sense that they generally form a three-dimensionalphysical crosslinked or entangled structure below the glass transitiontemperature (T_(g)) of the thermoplastic block portion such that theyexhibit elastic memories in response to external forces. The blockcopolymers are thermoplastic in the sense that they can be melted abovethe endblock T_(g), formed, and resolidified several times with littleor no change in physical properties (assuming a minimum of oxidativedegradation).

In such copolymers, the block portion A are the hard blocks and arederived from materials which have a sufficiently high glass transitiontemperature to form crystalline or glassy domains at the use temperatureof the polymer. Such hard blocks generally form strong physicalentanglements or agglomerates with other hard blocks in the copolymers.The hard block portion A generally comprises a polyvinylarene derivedfrom monomers such as styrene, α-methyl styrene, other styrenederivatives, or mixtures thereof. The hard block portion A may also be acopolymer derived from styrenic monomers such as those describedhereinabove and olefinic monomers such as ethylenes, propylenes,butylenes, isoprenes, butadienes, and mixtures thereof.

The hard block portion A preferably is polystyrene, having anumber-average molecular weight between from about 1,000 to about200,000, preferably from about 2,000 to about 100,000, more preferablyfrom about 5,000 to about 60,000. Typically the hard block portion Acomprises from about 10% to about 80%, preferably from about 20% toabout 50%, more preferably from about 25 to about 35% of the totalweight of the copolymer.

The material forming the B-block will have sufficiently low glasstransition temperature at the use temperature of the polymer such thatcrystalline or glassy domains are not formed at these workingtemperatures. The B-block may thus be regarded as a soft block. The softblock portion B is typically an olefinic polymer derived from conjugatedaliphatic diene monomers of from about 4 to about 6 carbon atoms orlinear alkene monomers of from about 2 to about 6 carbon atoms. Suitablediene monomers include butadiene, isoprene, and the like. Suitablealkene monomers include ethylene, propylene, butylene, and the like. Thesoft block portion B preferably comprises a substantially amorphouspolyolefin such as ethylene/propylene polymers, ethylene/butylenepolymers, polyisoprene, polybutadiene-, and the like or mixturesthereof. The number-average molecular weight of the soft block B istypically from about 1,000 to about 300,000, preferably from about10,000 to about 200,000, and more preferably from about 20,000 to about100,000. Typically the soft block portion B comprises from about 20% toabout 90%, preferably from about 50% to about 80%, more preferably fromabout 65% to about 75% of the total weight of the copolymer.

Suitable block copolymers for use in this invention comprise at leastone substantially elastomeric block portion B and at least onesubstantially thermoplastic block portions A. The block copolymers mayhave multiple blocks. In a preferred embodiment, the block copolymer maybe an A-B-A triblock copolymer, an A-B-A-B tetrablock copolymer, or anA-B-A-B-A pentablock copolymer. Also preferred for use herein aretriblock copolymers having an elastomeric midblock B and thermoplasticendblocks A and A′, wherein A and A′ may be derived from differentvinylarene monomers. Also useful in the present invention are blockcopolymers having more than one A block and/or more than one B block,wherein each A lock may be derived from the same or different vinylarenemonomers and each B block may be derived from the same or differentolefinic monomers. The block copolymers may also be radial, having threeor more arms, each arm being an B-A, B-A-B-A, or the like type copolymerand the B blocks being at or near the center portion of the radialpolymer. Good results may be obtained with, for example, four, five, orsix arms. The olefin block typically comprises at least about 50 percentby weight of the block copolymer. The unsaturation in olefinic doublebonds may be selectively hydrogenated, if desired, to reduce sensitivityto oxidative degradation and may have beneficial effects on theelastomeric properties. For example, a polyisoprene block can beselectively reduced to form an ethylene-propylene block. The vinylareneblock typically comprises at least about 10 percent by weight of theblock copolymer. However, higher vinylarene content is more preferredfor high elastic and low stress relaxation properties.

The block copolymer may be used in the elastomeric composition in anamount effective to achieve the desired elastic and low stressrelaxation properties. The block copolymer will generally be present inthe elastomeric composition in an amount typically from about 20 toabout 80 weight percent, preferably from about 30 to about 70 weightpercent, and more preferably from about 40 to about 60 weight percent ofthe elastomeric composition.

Suitable for use in the present invention are styrene-olefin-styrenetriblock copolymers such as styrene-butadiene-styrene (S-B-S),styrene-ethylene/butylene-styrene (S-EB-S),styrene-ethylene/propylene-styrene (S-EP-S), styrene-isoprene-styrene(S-I-S), hydrogenated polystyrene-isoprene/butadiene-styrene (S-IB-S)and mixtures thereof. The block copolymers may be employed alone, in ablend of block copolymers, or in a blend of one or more block copolymerswith one or more other substantially less elastomeric polymers such aspolypropylene, polyethylene, polybutadiene, polyisoprene, or mixturesthereof. The block copolymers employed preferably only have minorquantities of, and most preferably essentially no, such other polymerspresent.

Particularly preferred block copolymers for use herein arepolystyrene-ethylene/butylene-polystyrene block copolymers having astyrene content in excess of about 10 weight percent. With higherstyrene content, the polystyrene block portions generally have arelatively high molecular weight. Such linear block copolymers ofstyrene-ethylene/butylene-styrene (S-EB-S) are commercially availableunder the trade designation KRATON® G1600 series from the Shell ChemicalCompany, Huston, Tex. Also preferred for use herein arepolystyrene-ethylene-ethylene/propylene-styrene (S-E-EP-S) blockcopolymers, wherein the ethylene/propylene block is derived fromselective hydrogenation of the unsaturation sites within thepolystyrene-isoprene/butadiene-styrene block copolymers. Hydrogenatedpolystyrene-isoprene/butadiene-styrene (S-IB-S) block copolymers arecommercially available under the trade designation SEPTON® 4000 seriesfrom Kuraray America, Inc. New York, N.Y. All the styrenic-olefinicblock copolymers described herein are suitable for use in the low stressrelaxation elastomeric materials either alone or in mixtures thereof.

Various thermoplastic or substantially less elastomeric or blends may beused in the low stress relaxation elastomeric material of the presentinvention. Suitable thermoplastic polymers should preferably associatewith the hard blocks of the block copolymers to form an entangledthree-dimensional network. Not intending to be bound by theory, thisentangled network structure is believed to be capable of improving thetensile, elastic and stress relaxation properties. Thermoplasticpolymers such as polyphenylene oxide, and vinylarene resins derived frommonomers including styrene, α-methyl styrene, other styrene derivatives,vinyl toluene, and mixtures thereof, are useful in the presentinvention. These polymers are preferred because they are chemicallycompatible with the styrenic hard blocks of the block copolymer. It isbelieved to be advantageous for the components to be compatible suchthat they may more easily form an entangled three-dimensional networkstructure, and they do not physically separate to a significant extentfrom the network structure.

Thermoplastic polymers useful herein as the hard block associatingcomponent should have a molecular weight in the suitable range. Thethermoplastic polymers should preferably have an average molecularweight that is sufficiently high such that their glass transitiontemperature, tensile and elastic properties are increased. Thethermoplastic polymers useful herein should also have an averagemolecular weight not significantly different from that of the hardblocks of the elastomeric block copolymers so that they are compatiblewith the hard blocks. Suitable vinylarene resins should preferably havea number-average molecular weight of about 600 to about 200,000, morepreferably of about 5,000 to about 150,000, and most preferably fromabout 10,000 to about 100,000. Polystyrene is particularly preferred. Apreferred polystyrene has a number-average molecular weight of about40,000 to about 60,000, and is available under the tradename NOVACOR® PS200 series from Nova Chemicals, Inc., Monaca, Pa.

Not intending to be bound by theory, it is generally believed thatpolymers or resins useful as the hard block associating component shouldhave glass transition temperatures (Tg) higher than the use temperatureof the elastomeric material in order to “lock in” the three dimensionalnetwork structure and provide desired properties. As the gap between theuse temperature and the glass transition temperature narrows, thesepolymers may “disentangle” from the network structure and weaken thenetwork structure. Consequently, the tensile, elastic and stressrelaxation properties of the elastomeric material are negativelyaffected. These negative effects are especially pronounced in the stressrelaxation properties.

For body temperature applications such as absorbent articles, bandages,wraps or wound dressings, which would be worn next to a person's bodyfor an extended period of time, it is previously believed that polymershaving higher glass transition temperatures such as polyphenylene oxide,should be used. However, polyphenylene oxide is difficult to processbecause it has a high melting temperature and relatively high meltviscosity. Moreover, the high processing temperature required forpolyphenylene oxide may result in degradation of other components in theelastomeric materials or the final products. The initial modulus ofpolyphenylene oxide may also be too high for stretchable articles suchthat undue forces need to be applied in order to put the article on thewearer.

Since vinylarene resins have glass transition temperatures significantlylower than polyphenylene oxide, it is surprising to find that vinylareneresins can be used in the elastomeric materials of the present inventionto provide desired elastic and stress relaxation properties at bodytemperature under sustained load condition. Moreover, vinylarene resinsare easy to process at relatively low temperatures such that little orno degradation of other thermoplastic or elastomeric components wouldoccur.

Vinylarene resins useful herein as the hard block associating polymersshould preferably have a glass transition temperature ranges from about58° C. to about 180° C., more preferably from about 70° C. to about 150°C., more preferably from about 90° C. to about 130° C.

Also useful herein as the hard block associating polymer are lowmolecular weight aromatic hydrocarbon resins, either alone or in blendswith higher molecular weight polyvinylarenes, particularly polystyrene.The low molecular weight aromatic resins are preferably derived fromvinylarene monomers. The low molecular weight resins provide lowerviscosity, hence better processability of the elastomeric compositions.Not intending to be bound by theory, it is believed that the lowermolecular weight resins tend to be less effective in forming thethree-dimensional entanglements with the hard blocks of the elastomericcopolymers and polystyrene. And due to the low molecular weight, theresins may associate with either the elastomeric soft blocks or thethermoplastic hard blocks. In effect, incorporating the low molecularweight resins reduces the percentage of the hard, entangled networks inthe composition. Therefore, it is generally believed that low molecularweight resins may be used as processing aids, but they generally providenegative effects on the elastic and stress relaxation properties of thefilms prepared from compositions containing these resins. It issurprising to find that elastomeric compositions containing lowmolecular weight aromatic hydrocarbon resins, either alone or inmixtures with polystyrenes, exhibit the desired elastic and stressrelaxation properties suitable for use herein.

Typically, the ratios of polystyrene content to aromatic hydrocarbonresin content in the blends range from about 1:10 to about 10:1,preferably from about 1:4 to about 4:1. The number-average molecularweights of the aromatic hydrocarbon resins typically range from about600 to about 10,000. The preferred aromatic hydrocarbon resins have aglass transition temperature from about 60° C. to about 105° C. and anumber-average molecular weight of about 600 to about 4,000. Thepreferred aromatic hydrocarbon resins include ENDEX® 155 or 160,KRISTALEX® 3115 or 5140, PICCOTEX® 120 and PICCOLASTIC® D125, all areavailable from Hercules, Inc., Wilmington, Del.

The thermoplastic polymers or resin blends are generally in an amounttypically from about 3 to about 60 weight percent, preferably from about5 to about 40 weight percent, and more preferably from about 10 to about30 weight percent of the low stress relaxation elastomeric compositionused in the present invention.

Even though polystyrene, low molecular weight aromatic hydrocarbonresins and other endblock associating polymers or resins may providelower melt viscosity and promote processability of the composition, ithas been found that additional processing aid such as a hydrocarbon oil,is beneficial for further lowering the viscosity and enhancingprocessability. The oil decreases the viscosity of the elastomericcomposition such that the elastomeric composition becomes moreprocessable. However, the processing oil tends to decrease theelastomeric retention and tensile properties of the compositions.Typically, the processing oil is present in an amount up to about 60 wt%, preferably from about 5 to about 60 wt %, more preferably from about10 to about 50 wt %, and most preferably from about 15 to about 45 wt %of the elastomeric compositions.

In a preferred embodiment, the processing oil is compatible with thecomposition, and is substantially non-degrading at the processingtemperature. Suitable for use herein are hydrocarbon oils which may belinear, branched, cyclic, aliphatic or aromatic. Preferably theprocessing oil is a white mineral oil available under the tradenameBRITOL® from Witco Company, Greenwich, Conn. Also preferred as theprocessing oil is another mineral oil under the tradename DRAKEOL® fromPennzoil Company Penrenco Division, Karns City, Pa.

In general, an elastomeric composition with desirable elastic propertiesmay be prepared from a composition that comprises essentially only ablock copolymer. However, such a composition will generally be verydifficult to process because of high viscosity and high stretchy andtacky nature of the composition. In addition, the inherent tackiness ofthe elastomeric composition makes it difficult to handle. For example,the composition may be processed into a film which tends to stick to theprocessing equipment and is difficult to remove from the equipment, orwhen the composition have been processed and wound up, it tends to fusetogether and becomes very difficult to unwound for further processinginto the finished product.

It is found that blending the neat block copolymer with otherthermoplastic polymers as well as processing oils improves theprocessability and handling of the composition. The thermoplasticpolymers and processing oil tend to reduce the viscosity of thecomposition and provide improved processability of the composition. Tofurther improve the processability and handling of the composition,especially when a film of such elastomeric composition is desired, atleast one skin layer of a substantially less elastomeric material may belaminated with the elastomeric composition. In a preferred embodiment,the elastomeric composition is coextruded with thermoplasticcompositions to provide an elastomeric center layer between two skinlayers, each being substantially joined to one side of the center layer.The two skin layers may be of the same or different thermoplasticmaterials.

The skin layer is preferably at least partially compatible or misciblewith a component of the elastomeric block copolymers such that there issufficient adhesion between the center elastomeric layer and the skinlayer for further processing and handling. The skin layer may comprisethermoplastic polymers or blends of thermoplastic polymers andelastomeric polymers such that the skin layer is substantially lesselastomeric than the center elastomeric layer. Typically, the permanentset of the skin layer is at least about 20%, preferably at least about30%, more preferably at least about 40% greater than that of theelastomeric center layer. Thermoplastic polymers suitable for use as theskin layer may be a polyolefin derived from monomers such as ethylenes,propylenes, butylenes, isoprenes, butadienes, 1,3-pentadienes, α-alkenesincluding 1-butenes, 1-hexenes, and 1-octenes, and mixtures of thesemonomers, an ethylene copolymers such as ethylene-vinylacetatecopolymers (EVA), ethylene-methacrylate copolymers (EMA), andethylene-acrylic acid copolymers, a polystyrene, a poly(α-methylstyrene), a styrenic random block copolymer (such as INDEX®interpolymers, available form Dow Chemicals, Midland, Mich.), apolyphenylene oxide, and blends thereof Additionally, tie layers may beused to promote adhesion between the center elastomeric layer and thethermoplastic skin layer.

FIG. 5 is a plan view of alternative primary aperture shapes projectedin the plane of the first surface of an alternative elastomeric web ofthe present invention. While a repeating pattern of uniform shapes ispreferred, the shape of primary apertures, e.g., apertures 71, may begenerally circular, polygonal, or mixed, and may be arrayed in anordered pattern or in a random pattern. Although not shown, it isunderstood that the projected shape may also be elliptical, tear-dropshaped, or any other shape, that is, the present invention is believedto be aperture-shape independent.

The interconnecting elements are inherently continuous, with contiguousinterconnecting elements blending into one another in mutually-adjoiningtransition zones or portions, e.g., transition portions 87, shown inFIG. 5. In general, transition portions are defined by the largestcircle that can be inscribed tangent to any three adjacent apertures. Itis understood that for certain patterns of apertures the inscribedcircle of the transition portions may be tangent to more than threeadjacent apertures. For illustrative purposes, interconnecting membersmay be thought of as beginning or ending substantially at the centers ofthe transition portions, such as interconnecting members 97 and 98.Likewise, the sidewalls of the interconnecting members can be describedas interconnecting to sidewalls of contiguous interconnecting members atareas corresponding to points of tangency where the inscribed circle ofthe transition portion is tangent to an adjoining aperture.

Exclusive of the transition zones, cross-sections transverse to a centerline between the beginning and end of interconnecting members arepreferably of generally uniform U-shape. However, the transversecross-section need not be uniform along the entire length of theinterconnecting member, and for certain aperture configurations it willnot be uniform along most of its length. For example, as can beunderstood from the sectional illustrations of FIG. 5, forinterconnecting member 96, the width dimension, 86, of the base portion81 may vary substantially along the length of the interconnectingmember. In particular, in transition zones or portions 87,interconnecting members blend into contiguous interconnecting membersand transverse cross-sections in the transition zones or portions mayexhibit substantially non-uniform U-shapes, or no discernible U-shape.

Without wishing to be bound by theory, it is believed that the web ofthe present invention is more reliable (i.e., resistant to catastrophicfailure) when subjected to strain-induced stress due to the mechanismdepicted schematically in cross section in FIGS. 8A-8C and pictoriallyin photomicrographs 9-11. FIG. 8A shows a primary aperture 71 in plane102 of first surface 90, and a secondary aperture 72 in plane 106 ofsecond surface 85, remote from plane 106 of first surface 90, of web 80in an unstressed condition. When web 80 is stretched in the directiongenerally shown by arrows in FIG. 8B, first surface 90 is strained, andprimary aperture 71 is likewise strained into a deformed configuration.However, the perimeter of primary aperture 71 is formed by theinterconnecting members in a continuous first surface. Therefore,aperture 71 has no “edges” for tear initiation sites to compromise theelastic reliability of the web. The edges of the secondary aperture 72,being possible tear initiation sites, do not experience appreciablestrain-induced stresses until the web is strained to the point whereplane 102 is no longer remote from plane 106 of the first surface 90, asdepicted in FIG. 8C. At the point where planes 102 and 106 are no longerremote, web 80 begins to behave essentially as a planar, apertured web.

It is instructive to consider the ratio of overall web depth, “D” inFIG. 8A, to film thickness, “T” in FIG. 8A of an unstretched elastomericweb. This ratio of D/T may be termed the draw ratio, as it pertains tothe amount of film drawn out of the plane of the first surface due tothe forming process of the present invention. Applicant believes that,in general, an increase in the draw ratio serves to increase resistanceto tear by placing the second surface more remote from the firstsurface.

Without wishing to be bound by theory, it is believed that when the web80 is strained or stretched, the elastomeric layer 101 of the presentinvention allows the base 81 of the interconnecting members forming acontinuous web in the continuous first surface 90 to stretch. Skin layer103 helps maintain the three-dimensional nature of the web, despite theapplied stress, allowing the strain on the continuous first surface 90and the resulting deformation of primary apertures 71 to be at leastpartially dissociated from the discontinuous second surface therebyminimizing strain at secondary apertures 72. Therefore thestrain-induced stress at the continuous first surface of the web issubstantially decoupled from potential strain-induced stress at tearinitiation sites on the discontinuous second surface, at least until thesecondary apertures begin to enter the plane of the first surface. Thissubstantial dissociation, or decoupling, of the strain-induced stress ofthe web from strain-induced stress at the secondary aperturessignificantly increases web reliability by allowing repeated andsustained strains of the web up to about 400% or more without failure ofthe web due to tear initiation at the apertures.

The photomicrographs of FIGS. 9-11 are believed to depict visually themechanism described schematically in FIGS. 8A-8 C. FIG. 9 is an opticalphotomicrograph showing the first surface and primary apertures of a webformed according the method described herein. In an as-formed,unextended configuration the continuous first surface of the webembodiment shown in FIG. 9 generally forms a regular pattern of 1 mmsquare primary apertures spaced about 1 mm apart on all sides. FIGS. 10and 11 are scanning electron microscope photomicrographs showing thediscontinuous second surface of the web embodiment of FIG. 9, shown at aslightly different scale. FIG. 10 shows the second surface of anelastomeric web generally in a plane remote from the plane of the firstsurface in an unstretched state. FIG. 11 shows the second surface of aweb in a state of approximately 100% elongation. As shown in FIG. 11,the edges of the secondary apertures remain remote from the plane of thefirst surface. Although some distortion of the secondary apertures takesplace, the edges remain in a substantially unstressed condition. Again,it is this substantial decoupling of the strain-induced stress of theweb from strain-induced stress at the secondary apertures thatsignificantly increases web reliability.

The differential elastic behavior of planar multilayer films or fibershaving a relatively less elastic skin layer stretched beyond its elasticlimit is known in the art, as described in the aforementioned U.S.Patent to Krueger et al., as well as in U.S. Pat. No. 5,376,430 toSwenson et al., issued Dec. 27, 1994 and U.S. Pat. No. 5,352,518 toMuramoto et al., issued Oct. 4, 1994. As shown in the art, upon recoveryafter extension beyond the elastic limits of the skin layer, the skinlayer may form a microscopic microtexture of peak and valleyirregularities, due to the resulting increased surface area of the skinlayer relative to the elastomeric layer.

Likewise, when a web of the present invention is strained for the firsttime, the skin layer of the strained portion may be stressed beyond itselastic limit. The elastomeric layer allows the web to returnsubstantially to its pre-stressed, macroscopic, three-dimensionalconfiguration, but the portions of the skin layer that were stressedbeyond their elastic limit may not return to a pre-stressedconfiguration due to the excess material created in the inelasticstrain. Upon recovery after extension, the skin layer forms microscopicmicrotexture of peak and valley irregularities, more generally describedas transversely-extending rugosities, as shown in the photomicrograph ofFIG. 12. The rugosities form on the interconnecting members insubstantially uniform patterns generally transverse to the direction ofstretch, and generally radially disposed about the primary apertures.Depending on the degree of strain on the web, the rugosities may belimited to substantially the continuous first surface of the web, ormore generally may extend over substantially the entire surface of theinterconnecting members.

Without being bound by theory, it is believed that thetransversely-extending rugosities are beneficial to the elastomeric webfor at least two reasons. First, the rugosities impart a softer overalltexture or feel to the elastomeric web. Second, the rugosities, beingradially disposed to the primary apertures, and extending toward thesecondary apertures, may facilitate better fluid handlingcharacteristics when used as a body-contacting web. of a disposableabsorbent article.

A representative embodiment of an elastomeric web of the presentinvention utilized in a disposable absorbent article in the form of adiaper 400, is shown in FIG. 13. As used herein, the term “diaper”refers to a garment generally worn by infants and incontinent personsthat is worn about the lower torso of the wearer. It should beunderstood, however, that the clastomeric web of the present inventionis also applicable to other absorbent articles such as incontinentbriefs, training pants, sanitary napkins, and the like. The diaper 400depicted in FIG. 13 is a simplified absorbent article that couldrepresent a diaper prior to its being placed on a wearer. It should beunderstood, however, that the present invention is not limited to theparticular type or configuration of diaper shown in FIG. 13. Aparticularly preferred representative embodiment of a disposableabsorbent article in the form of a diaper is taught in U.S. Pat. No.5,151,092, to Buell et al., issued Sep. 29, 1992, being herebyincorporated herein by reference.

FIG. 13 is a perspective view of the diaper 400 in its uncontractedstate (i.e., with all the elastic induced contraction removed) withportions of the structure being cut-away to more clearly show theconstruction of the diaper 400. The portion of the diaper 400 whichcontacts the wearer faces the viewer. The diaper 400 is shown in FIG. 13to preferably comprise a liquid pervious topsheet 404; a liquidimpervious backsheet 402 joined with the topsheet 404; and an absorbentcore 406 positioned between the topsheet 404 and the backsheet 402.Additional structural features such as elastic leg cuff members andfastening means for securing the diaper in place upon a wearer may alsobe included.

While the topsheet 404, the backsheet 402, and the absorbent core 406may be assembled in a variety of well known configurations, preferreddiaper configurations are described generally in U.S. Pat. No. 3,860,003entitled “Contractible Side Portions for Disposable Diaper” which issuedto Kenneth B. Buell on Jan. 14, 1975; U.S. Pat. No. 5,151,092 issued toBuell on Sep. 9, 1992; and U.S. Pat. No. 5,221,274 issued to Buell onJun. 22, 1993; and U.S. Pat. No. 5,554,145 entitled “Absorbent ArticleWith Multiple Zone Structural Elastic-Like Film Web Extensible WaistFeature” which issued to Roe et al. on Sep. 10, 1996; U.S. Pat. No.5,569,234 entitled “Disposable Pull-On Pant” which issued to Buell etal. on Oct. 29, 1996; U.S. Pat. No. 5,580,411 entitled “Zero ScrapMethod For Manufacturing Side Panels For Absorbent Articles” whichissued to Nease et al. on Dec. 3, 1996, and U.S. patent application Ser.No. 08/915,471 now U.S. Pat. No. 6,004,306 entitled “Absorbent ArticleWith Multi-Directional Extensible Side Panels” filed Aug. 20, 1997 inthe name of Roble et al.; each of which is incorporated herein byreference.

FIG. 13 shows a representative embodiment of the diaper 400 in which thetopsheet 404 and the backsheet 402 are co-extensive and have length andwidth dimensions generally larger than those of the absorbent core 406.The topsheet 404 is joined with and superimposed on the backsheet 402thereby forming the periphery of the diaper 400. The periphery definesthe outer perimeter or the edges of the diaper 400. The peripherycomprises the end edges 401 and the longitudinal edges 403.

The size of the backsheet 402 is dictated by the size of the absorbentcore 406 and the exact diaper design selected. In a preferredembodiment, the backsheet 402 has a modified hourglass-shape extendingbeyond the absorbent core 406 a minimum distance of at least about 1.3centimeters to about 2.5 centimeters (about 0.5 to about 1.0 inch)around the entire diaper periphery.

The topsheet 404 and the backsheet 402 are joined together in anysuitable manner. As used herein, the term “joined” encompassesconfigurations whereby the topsheet 404 is directly joined to thebacksheet 402 by affixing the topsheet 404 directly to the backsheet402, and configurations whereby the topsheet 404 is indirectly joined tothe backsheet 402 by affixing the topsheet 404 to intermediate memberswhich in turn are affixed to the backsheet 402. In a preferredembodiment, the topsheet 404 and the backsheet 402 are affixed directlyto each other in the diaper periphery by attachment means (not shown)such as an adhesive or any other attachment means as known in the art.For example, a uniform continuous layer of adhesive, a patterned layerof adhesive, or an array of separate lines or spots of adhesive can beused to affix the topsheet 404 to the backsheet 402.

End edges 401 form a waist region, which in a preferred embodimentcomprise a pair of elastomeric side panels 420, which extend laterallyfrom end edges 401 of diaper 400 in an extended configuration. In apreferred embodiment elastomeric side panels 420 comprise theelastomeric web of the present invention. In an especially preferredembodiment, when used as elastomeric side panels, the web of the presentinvention is further processed to form a composite laminate by bondingit on one, or preferably both sides thereof, with fibrous nonwovenmaterials to form a soft, compliant elasticized member, utilizingmethods known in the art, such as adhesive bonding.

Fibrous nonwoven materials suitable for use in a composite laminate ofthe present invention include nonwoven webs formed of synthetic fibers(such as polypropylene, polyester, or polyethylene), natural fibers(such as wood, cotton, or rayon), or combinations of natural andsynthetic fibers. Suitable nonwoven materials can be formed by variousprocesses such as carding, spun-bonding, hydro-entangling, and otherprocesses familiar to those knowledgeable in the art of nonwovens. Apresently preferred fibrous nonwoven material is carded polypropylene,commercially available from Fiberweb of Simpsonville, S.C.

Fibrous nonwoven materials may be bonded to the elastomeric web by anyone of various bonding methods known in the art. Suitable bondingmethods include adhesive bonding such as by a uniform continuous layerof adhesive, a patterned layer of adhesive, or an array of separatelines, spirals, or spots of adhesive, or other methods such as heatbonds, pressure bonds, ultrasonic bonds, dynamic mechanical bonds, orany other suitable attachment means or combinations of these attachmentmeans as are known in the art. Representative bonding methods are alsodescribed in U.S. SIR No. H1670, entitled “Absorbent Article Having aNonwoven and Apertured Film Coversheet” by Aziz et al., published Jul.1, 1997, and being hereby incorporated herein by reference.

After bonding to a fibrous nonwoven material, the composite web may tendto be less elastomeric due to the relative inelasticity of the bondednonwoven. To render the nonwoven more elastic, and to restore elasticityto the composite laminate, the composite web may be processed by methodsand apparatus used for elasticizing “zero strain” laminates byincremental stretching, as disclosed in the aforementioned Buell et al.'092 patent, as well as the aforementioned Weber et al. '897, Buell etal. '793, and Weber et al. '679 patents. The resulting elasticized“zero-strain” composite web then has a soft, cloth-like feel forextended use and comfortable fit in an absorbent garment.

Side panels 420 may be joined to the diaper in any suitable manner knownin the art. For example, as shown in FIG. 13, side panels 420 may beaffixed directly to the backsheet 402 by attachment means (not shown)such as an adhesive or any other attachment means as known in the art. Aparticularly preferred configuration for side panels 420 is shown inFIG. 14, a configuration which is more fully disclosed in commonlyassigned U.S. Pat. No. 5,669,897, issued Sep. 23, 1997 to LaVon et al.,and U.S. patent application Ser. No. 08/155,048, filed Nov. 19, 1993 byRoles et al., now abandoned; the disclosures of both being herebyincorporated herein by reference.

As shown in FIG. 14, side panel 420 is preferably comprised of two websor strips, 421 and 422. Strips 421 and 422 may be two discrete strips,or alternatively they may be formed by bending a single strip at leadingedge 424, and offsetting the two resulting strip lengths in anon-parallel manner. If two discrete strips are used, they may bebonded, as with suitable adhesive, to one another at leading edge 424,and may simultaneously be bonded to tape tab 423. Side panel 420 may bebonded to backsheet 402 at bond area 425 in any suitable manner, andparticularly as disclosed in the aforementioned LaVon et al. '879patent. While it is not necessary that the pairs of side panels beidentical, they are preferably mirror images one of the other. Otherexamples of diapers with elasticized side panels are disclosed in U.S.Pat. No. 4,857,067, entitled “Disposable Diaper Having Shirred Ears”issued to Wood, et al. on Aug. 15, 1989; U.S. Pat. No. 4,381,781 issuedto Sciaraffa, et al. on May 3, 1983; U.S. Pat. No. 4,938,753 issued toVan Gompel, et al. on Jul. 3, 1990; the herein before referenced U.S.Pat. No. 5,151,092 issued to Buell on Sep. 9, 1992; and U.S. Pat. No.5,221,274 issued to Buell on Jun. 22, 1993; U.S. Pat. No. 5,669,897issued to LaVon, et al. on Sep. 23, 1997 entitled “Absorbent ArticlesProviding Sustained Dynamic Fit”; U.S. Pat. No. 5,897,545 issued toKline, et. al. on Apr. 27, 1999; U.S. patent application Ser. No.08/155,048 entitled “Absorbent Article With Multi-Directional ExtensibleSide Panels” filed Nov. 19, 1993 in the names of Roble, et al. nowabandoned; each of which is incorporated herein by reference.

The diaper 400 may also include a fastening system 423. The fasteningsystem 423 preferably maintains waist regions 401 in an overlappingconfiguration so as to provide lateral tensions about the circumferenceof the diaper 400 to hold the diaper 400 on the wearer. The fasteningsystem 423 preferably comprises tape tabs and/or hook and loop fasteningcomponents, although any other known fastening means are generallyacceptable. Some exemplary fastening systems are disclosed in U.S. Pat.No. 3,848,594 entitled “Tape Fastening System for Disposable Diaper”issued to Buell on Nov. 19, 1974; U.S. Pat. No. 4,662,875 entitled“Absorbent Article” issued to Hirotsu et al. on May 5, 1987; U.S. Pat.No. 4,846,815 entitled “Disposable Diaper Having An Improved FasteningDevice” issued to Scripps on Jul. 11, 1989; U.S. Pat. No. 4,894,060entitled “Disposable Diaper With Improved Hook Fastener Portion” issuedto Nestegard on Jan. 16, 1990; U.S. Pat. No. 4,946,527 entitled“Pressure-Sensitive Adhesive Fastener And Method of Making Same” issuedto Battrell on Aug. 7, 1990; and the herein before referenced U.S. Pat.No. 5,151,092 issued to Buell on Sep. 9, 1992; and U.S. Pat. No.5,221,274 issued to Buell on Jun. 22, 1993. The fastening system mayalso provide a means for holding the article in a disposal configurationas disclosed in U.S. Pat. No. 4,963,140 issued to Robertson et al. onOct. 16, 1990. The fastening system may also include primary andsecondary fastening systems, as disclosed in U.S. Pat. No. 4,699,622 toreduce shifting of overlapped portions or to improve fit as disclosed inU.S. Pat. Nos. 5,242,436; 5,499,978; 5,507,736; 5,591,152. Each Of thesepatents is incorporated herein by reference. In alternative embodiments,opposing sides of the garment may be seamed or welded to form a pant.This allows the article to be used as a pull-on diaper or training pant.

Other elastic members (not shown), of the present invention may bedisposed adjacent the periphery of the diaper 400. Elastic members arepreferably along each longitudinal edge 403, so that the elastic memberstend to draw and hold the diaper 400 against the legs of the wearer. Inaddition, the elastic members can be disposed adjacent either or both ofthe end edges 401 of the diaper 400 to provide a waistband as well as orrather than leg cuffs. For example, a suitable waistband is disclosed inU.S. Pat. No. 4,515,595 to Kievit et al., issued May 7, 1985, thedisclosure of which is hereby incorporated by reference. In addition, amethod and apparatus suitable for manufacturing a disposable diaperhaving elastically contractible elastic members is described in U.S.Pat. No. 4,081,301 to Buell, issued Mar. 28, 1978, the disclosure ofwhich is hereby incorporated herein by reference.

The elastic members are secured to the diaper 400 in an elasticallycontractible condition so that in a normally unrestrained configuration,the elastic members effectively contract or gather the diaper 400. Theelastic members can be secured in an elastically contractible conditionin at least two ways. For example, the elastic members can be stretchedand secured while the diaper 400 is in an uncontracted condition. Inaddition, the diaper 400 can be contracted, for example, by pleating,and the elastic members secured and connected to the diaper 400 whilethe elastic members are in their relaxed or unstretched condition. Theelastic members may extend along a portion of the length of the diaper400. Alternatively, the elastic members can extend the entire length ofthe diaper 400, or any other length suitable to provide an elasticallycontractible line. The length of the elastic members is dictated by thediaper design.

The elastic members can be in a multitude of configurations. Forexample, the width of the elastic members can be varied from about 0.25millimeters (0.01 inches) to about 25 millimeters (1.0 inch) or more;the elastic members can comprise a single strand of elastic material orcan comprise several parallel or non-parallel strands of elasticmaterial; or the elastic members can be rectangular or curvilinear.Still further, the elastic members can be affixed to the diaper in anyof several ways which are known in the art. For example, the elasticmembers can be ultrasonically bonded, heat and pressure sealed into thediaper 400 using a variety of bonding patterns or the elastic memberscan simply be glued to the diaper 400.

As shown in FIG. 13, the absorbent core 406 preferably includes a fluiddistribution member 408. In a preferred configuration such as depictedin FIG. 13, the absorbent core 406 preferably further includes anacquisition layer or member 410 in fluid communication with the fluiddistribution member 408 and located between the fluid distributionmember 408 and the topsheet 404. The acquisition layer or member 410 maybe comprised of several different materials including nonwoven or wovenwebs of synthetic fibers including polyester, polypropylene, orpolyethylene, natural fibers including cotton or cellulose, blends ofsuch fibers, or any equivalent materials or combinations of suchmaterials.

In use, the diaper 400 is applied to a wearer by positioning the backwaistband region under the wearer's back, and drawing the reminder ofthe diaper 400 between the wearer's legs so that the front waistbandregion is positioned across the front of the wearer. The elastomericside panels are then extended as necessary for comfort and fit, and thetape-tab or other fasteners are then secured preferably to outwardlyfacing areas of the diaper 400. By having side panels 420 comprising anelastomeric web of the present invention, the diaper may be adapted fordiffering sizes of children, for example, in a manner providing forclose, comfortable fit with breathability.

While a disposable diaper is shown as a preferred embodiment of agarment comprising an elastomeric web of the present invention, thisdisclosure is not meant to be limiting to disposable diapers. Otherdisposable garments may also incorporate an elastomeric web of theinvention in various parts to give added comfort, fit and breathability.As well, it is contemplated that even durable garments such asundergarments and swimwear may benefit from the durable porous,extensible characteristics of an elastomeric web of the presentinvention.

The multilayer film 120 of the present invention may be processed usingconventional procedures for producing multilayer films on conventionalcoextruded film-making equipment. In general, polymers can be meltprocessed into films using either cast or blown film extrusion methodsboth of which are described in “Plastics Extrusion Technology” 2nd Ed.,by Allan A. Griff (Van Nostrand Reinhold-1976), which is herebyincorporated herein by reference. Cast film is extruded through a linearslot die. Generally, the flat web is cooled on a large moving polishedmetal roll. It quickly cools, and peels off the first roll, passes overone or more auxiliary rolls, then through a set of rubber-coated pull or“haul-off” rolls, and finally to a winder.

In blown film extrusion the melt is extruded upward through a thinannular die opening. This process is also referred to as tubular filmextrusion. Air is introduced through the center of the die to inflatethe tube and causes it to expand. A moving bubble is thus formed whichis held at constant size by control of internal air pressure. The tubeof film is cooled by air blown through one or more chill ringssurrounding the tube. The tube is next collapsed by drawing it into aflattened frame through a pair of pull rolls and into a winder.

A coextrusion process requires more than one extruder and either acoextrusion feedblock or a multi-manifold die system or combination ofthe two to achieve the multilayer film structure. U.S. Pat. Nos.4,152,387 and 4,197,069, issued May 1, 1979 and Apr. 8, 1980,respectively, both to Cloeren, are hereby incorporated herein byreference, disclose the feedblock principle of coextrusion. Multipleextruders are connected to the feedblock which employs moveable flowdividers to proportionally change the geometry of each individual flowchannel in direct relation to the volume of polymer passing through saidflow channels. The flow channels are designed such that at their pointof confluence, the materials flow together at the same flow rate andpressure eliminating interfacial stress and flow instabilities. Once thematerials are joined in the freedblock, they flow into a single manifolddie as a composite structure. It is important in such processes that themelt viscosities and melt temperatures of the material do not differ toogreatly. Otherwise flow instabilities can result in the die leading topoor control of layer thickness distribution in the multilayer film.

An alternative to feedblock coextrusion is a multi-manifold or vane dieas disclosed in aforementioned U.S. Pat. Nos. 4,152,387, 4,197,069, aswell as U.S. Pat. No. 4,533,308, issued Aug. 6, 1985 to Cloeren, herebyincorporated herein by reference. Whereas in the freedblock system meltstreams are brought together outside and prior to entering the die body,in a multi-manifold or vane die each melt stream has its own manifold inthe die where the polymers spread independently in their respectivemanifolds. The melt streams are married near the die exit with each meltstream at full die width. Moveable vanes provide adjustability of theexit of each flow channel in direct proportion to the volume of materialflowing through it, allowing the melts to flow together at the samelinear flow rate, pressure, and desired width.

Since the melt flow properties and melt temperatures of polymers varywidely, use of a vane die has several advantages. The die lends itselftoward thermal isolation characteristics wherein polymers of greatlydiffering melt temperatures, for example up to 175° F. (80° C.), can beprocessed together.

Each manifold in a vane die can be designed and tailored to a specificpolymer. Thus the flow of each polymer is influenced only by the designof its manifold, and not forces imposed by other polymers. This allowsmaterials with greatly differing melt viscosities to be coextruded intomultilayer films. In addition, the vane die also provides the ability totailor the width of individual manifolds, such that an internal layercan be completely surrounded by the outer layer leaving no exposededges. The aforementioned patents also disclose the combined use offeedblock systems and vane dies to achieve more complex multilayerstructures.

The multilayer films of the present invention may comprise two or morelayers, at least one of the layers being elastomeric. It is alsocontemplated that multiple elastomeric layers may be utilized, eachelastomeric layer being joined to one or two skin layers. In athree-layer film, core layer 101 has opposed first and second sides, oneside being substantially continuously joined to one side of each outerskin layer 103 prior to the application of applied stress to the web.Three-layer films, like multilayer film 120 shown in FIG. 4, preferablycomprise a central elastomeric core 101 that may comprise from about 10to 90 percent of the total thickness of the film. Outer skin layers 103are generally, but not necessarily, identical and may comprise fromabout 5 to 45 percent of the total thickness of the film. Although anelastomeric layer is generally substantially joined to one or two skinlayers without the use of adhesives, adhesives or tie layers may be usedto promote adherence between the layers. Tie layers, when employed, mayeach comprise from about 5 to 10 percent of the total film thickness.

After the multilayer elastomeric film has been coextruded it ispreferably fed to a forming structure for aperturing and cooling,thereby producing a macroscopically-expanded, three-dimensional,apertured elastomeric web of the present invention. In general the filmmay be formed by drawing such film against a forming screen or otherforming structure by means of a vacuum and passing an air or waterstream over the outwardly posited surface of the film. Such processesare described in the aforementioned Radel et al. patent as well as inU.S. Pat. No. 4,154,240, issued to Lucas et al., both herebyincorporated herein by reference. Forming a three-dimensionalelastomeric web may alternatively be accomplished by applying a liquidstream with sufficient force and mass flux to cause the web formation asdisclosed in commonly assigned U.S. Pat. No. 4,695,422, issued to Curroet al. and hereby incorporated herein by reference. Alternatively, thefilm can be formed as described in commonly assigned U.S. Pat. No.4,552,709 to Koger et al., and hereby incorporated herein by reference.Preferably the elastomeric web is uniformly macroscopically expanded andapertured by the method of supporting the forming structure in a fluidpressure differential zone by a stationary support member as taught bycommonly assigned U.S. Pat. Nos. 4,878,825 and 4,741,877, both toMullane, Jr., and hereby incorporated herein by reference.

Although not shown, the process of the present invention, using aconventional forming screen having a woven wire support structure, wouldalso form a web within the scope of the present invention. The knucklesof a woven wire forming screen would produce a macroscopically-expanded,three-dimensional web having a pattern of undulations in the firstsurface, the undulations corresponding to the knuckles of the screen.However, the undulations would remain generally in the plane of thefirst surface, remote from the plane of the second surface. Thecross-section of the interconnecting members would remain generallyupwardly concave-shaped with the interconnecting sidewalls of theinterconnecting members terminating to form secondary aperturessubstantially in the plane of the second surface.

A particularly preferred forming structure comprises a photoetchedlaminate structure as shown in FIG. 15, showing an enlarged, partiallysegmented, perspective illustration of a photoetched laminate structureof the type used to form plastic webs of the type generally illustratedin FIG. 2. The laminate structure 30 is preferably constructed generallyin accordance with the teachings of the aforementioned Radel et al.patent, and is comprised of individual lamina 31, 32, and 33. Acomparison of FIG. 3 with the elastomeric web 80 shown in FIG. 2 revealsthe correspondence of primary aperture 71 in plane 102 of theelastomeric web 80 to opening 61 in the uppermost plane 62 of thephotoetched laminate structure 30. Likewise, aperture opening 72 inplane 106 of elastomeric web 80 corresponds to opening 63 in lowermostplane 64 of photoetched laminate structure 30.

The uppermost surface of photoetched laminate structure 30 located inuppermost plane 62 may be provided with a microscopic pattern ofprotuberances 48 without departing from the scope of the presentinvention. This is preferably accomplished by applying a resist coatingwhich corresponds to the desired microscopic pattern of surfaceaberrations to the top side of a planar photoetched lamina 31, andthereafter initiating a second photoetching process. The secondphotoetching process produces a lamina 31 having a microscopic patternof protuberances 48 on the Uppermost surface of the interconnectedelements defining the pentagonally shaped apertures, e.g., aperture 41.The microscopic pattern of protuberances does not substantially removethe first surface from the plane of the first surface. The first surfaceis perceived on a macroscopic scale, while the protuberances areperceived on a microscopic scale. Construction of a laminate structureemploying such a pattern of protuberance 48 on its uppermost layer isgenerally disclosed in the aforementioned Ahr et al. patent.

Processes for constructing laminate structures of the type generallydisclosed in FIG. 2 are disclosed in the aforementioned Radel et al.patent. The photoetched laminate structures are preferably rolled byconventional techniques into a tubular forming member 520, asillustrated generally in FIG. 16 and their opposing ends joinedgenerally in accordance with the teachings of Radel et al. to produce aseamless tubular forming member 520.

The outermost surface 524 of the tubular forming member 520 is utilizedto form the multilayer elastomeric web brought in contact therewithwhile the innermost surface 522 of the tubular member generally does notcontact the plastic web during the forming operation. The tubular membermay, in a preferred embodiment of the present invention, be employed asthe forming surface on debossing/perforating cylinder 555 in a processof the type described in detail in the aforementioned Lucas et al.patent. A particularly preferred apparatus 540 of the type disclosed insaid patent is schematically shown in FIG. 17. It includes debossing andperforating means 543, and constant tension film forwarding and windingmeans 545 which may, if desired, be substantially identical to andfunction substantially identically to the corresponding portions of theapparatus shown and described in U.S. Pat. No. 3,674,221 issue toRiemersma on Jul. 4, 1972 and which is hereby incorporated herein byreference. The frame, bearing, supports and the like which mustnecessarily be provided with respect to the functional members ofapparatus 540 are not shown or described in detail in order to simplifyand more clearly depict and disclose the present invention, it beingunderstood that such details would be obvious to persons of ordinaryskill in the art of designing plastic film converting machinery.

Briefly, apparatus 540, schematically shown in FIG. 17, comprises meansfor continuously receiving a ribbon of thermoplastic film 550 fromcoextruder 559, for example, and converting it into a debossed andperforated film 551. Film 550 is preferably supplied directly from thecoextrusion process while still above its thermoplastic temperature soas to be vacuumed formed prior to cooling. Alternatively, film 550 maybe heated by directing hot air jets against one surface of the filmwhile applying vacuum adjacent the opposite surface of the film. Tomaintain sufficient control of film 550 to substantially obviatewrinkling and/or macroscopically distending the film, apparatus 540comprises means for maintaining constant machine direction tension inthe film both upstream and downstream of a zone where the temperature isgreater than the thermoplastic temperature of the film, but in whichzone there is substantially zero machine direction and cross-machinedirection tension tending to macroscopically distend the film. Thetension is required to control and smooth a running ribbon ofthermoplastic film; the zero tension zone result from the film in thezone being at a sufficiently high temperature to enable debossing andperforating the film.

As can be seen in FIG. 17, the debossing and perforating means 543includes a rotatably mounted debossing perforating cylinder 555 havingclosed ends 580, a nonrotating triplex vacuum manifold assembly 556 andoptional hot air jet means (not shown). The triplex vacuum manifoldassembly 556 comprises three manifolds designated 561, 562, and 563.Also shown in FIG. 17 is a power rotated lead-off/chill roll 566 and asoft-face (e.g., low density neoprene) roll 567 which is driven with thechill roll. Briefly, by providing means (not shown) for independentlycontrolling the degree of vacuum in the three vacuum manifolds, athermoplastic ribbon of film running circumferentially about a portionof the debossing-perforating cylinder 555 is sequentially subjected to afirst level of vacuum by manifold 561, a second level of vacuum bymanifold 562, and a third level of vacuum by manifold 563. As will bedescribed more fully hereinafter, the vacuum applied to the film bymanifold 561 enables maintaining upstream tension in the film, vacuumapplied by manifold 562 enables perforating the film, and vacuum appliedby manifold 563 enables cooling the film to below its thermoplastictemperature and enables establishing downstream tension therein. Ifdesired, the film contacting surface of the debossing-perforatingcylinder 555 may be preheated prior to reaching vacuum manifold 562 bymeans well known in the art (and therefore not shown) to facilitatebetter conformance of plastic films comprised of flow-resistant polymersduring the debossing operation. The nip 570 intermediate chill roll 566and the soft-face roll 567 is only nominally loaded because highpressure would iron-out the three-dimensional debossments which areformed in the film in the aforementioned manner. However, even nominalpressure in nip 570 helps the vacuum applied by manifold 563 to isolatedownstream tension (i.e., roll winding tension) from thedebossing-perforating portion of the debossing-perforating cylinder 555,and enables the nip 570 to peel the debossed and perforated film fromthe debossing-perforating cylinder 555. Moreover, while vacuum drawnambient air passing through the film into manifold 563 will normallycool the film to below its thermoplastic temperature, the passage ofcoolant through the chill roll as indicated by arrows 573, 574 in FIG.17 will enable the apparatus to handle thicker films or be operated athigher speeds.

The debossing and perforating means 543 comprises the rotatably mounteddebossing-perforating cylinder 555, means (not shown) for rotating thecylinder 555 at a controlled peripheral velocity, the non-rotatingtriplex vacuum manifold assembly 556 inside the debossing-perforatingcylinder 555, means (not shown) for applying controlled levels of vacuuminside the three vacuum manifolds 561, 562 and 563 comprising thetriplex manifold assembly 556, and optional hot air jet means (notshown). The debossing-perforating cylinder 555 may be constructed bygenerally following the teachings of the aforementioned Lucas et al.patent, but substituting a tubular laminate forming surface of thepresent invention for the perforated tubular forming surface disclosedtherein.

To summarize, the first vacuum manifold 561, and the third vacuummanifold 563 located within the debossing-perforating cylinder 555enable maintaining substantially constant upstream and downstreamtension, respectively, in a running ribbon of film while theintermediate portion of the film adjacent the second vacuum manifold 562within the debossing-perforating cylinder 555 is subjected to tensionvitiating heat and vacuum to effect debossing and perforating of thefilm.

While a preferred application of the disclosed photoetched laminatestructure is in a vacuum film forming operation as generally outlined inthe aforementioned commonly assigned patent issued to Lucas et al., itis anticipated that photoetched laminate forming structures of thepresent invention could be employed with equal facility to directly forma three-dimensional plastic structure of the present invention. Such aprocedure would involve applying a heated fluid plastic material,typically a thermoplastic resin, directly to the forming surfaceapplying a sufficiently great pneumatic differential pressure to theheated fluid plastic material to cause said material to conform to theimage of the perforate laminate forming surface, allowing the fluidmaterial to solidify, and thereafter removing the three-dimensionalplastic structure from the forming surface.

While the web embodiment generally disclosed in FIG. 2 represents aparticularly preferred embodiment of the present invention, any numberof interconnecting members may be employed within web structures of thepresent invention, e.g., secondary, tertiary, etc. An example of such astructure is shown in FIG. 18 which also shows a variant of upwardlyconcave-shaped cross-sections of interconnecting members. The aperturenetwork shown in FIG. 18 comprises a primary aperture 301 formed by amultiplicity of primary interconnecting elements, e.g., elements 302,303, 304 and 305 interconnected to one another in uppermost plane 307 ofthe web 300, said opening being further subdivided into smallersecondary apertures 310 and 311 by secondary interconnecting member 313at an intermediate plane 314. Primary aperture 310 is further subdividedby tertiary interconnecting member 320 into even smaller secondaryapertures 321 and 322, respectively, at a still lower plane 325 withinweb 300. As can be seen from FIG. 19, which is taken along section line19—19 of FIG. 18, planes 314 and 325 are generally parallel to andlocated intermediate uppermost plane 307 and lowermost plane 330.

In the web embodiment illustrated in FIG. 17 and 18, the primary andsecondary interconnecting members are further connected to intersectingtertiary interconnecting members, e.g., tertiary interconnecting members320, which also exhibit a generally upwardly concave-shapedcross-section along their length. The intersecting primary, secondaryand tertiary interconnecting members terminate substantiallyconcurrently with one another in the plane 330 of the second surface 332to form a multiplicity of openings or apertures in the web's secondsurface, e.g., apertures 370, 371 and 372. It is clear that theinterconnected primary, secondary and tertiary interconnecting memberslocated between the first and second surfaces of the web 300 form aclosed network connecting each of the primary apertures, e.g., aperture301 in the first surface 331 of the web, with a multiplicity ofsecondary apertures, e.g., apertures 370, 371 and 372, in the secondsurface 332 of the web.

As will be appreciated, the generally upwardly concave-shapedinterconnecting members utilized in webs of the present invention may besubstantially straight along their entire length. Alternatively, theymay be curvilinear, they may comprise two or more substantially straightsegments or they may be otherwise oriented in any desired directionalong any portion of their length. There is no requirement that theinterconnecting members be identical to one another. Furthermore, theaforementioned shapes may be combined in any desired fashion to producewhatever pattern is desired. Regardless of the shape ultimatelyselected, the upwardly concave-shaped cross-section which exists alongthe respective lengths of the interconnected interconnecting membershelps impart resilience to elastomeric webs of the present invention, aswell as three-dimensional standoff.

It will be obvious to those skilled in the art that various changes andmodifications can be made without departing from the spirit and scope ofthe present invention. For example, in the event it is desired toproduce webs of the present invention wherein a predetermined portion ofthe web is capable of preventing fluid transmission, it is feasible toperform the debossing operation without causing rupture of the web inits second surface. Commonly assigned U.S. Pat. No. 4,395,215 issued toBishop on Jul. 26, 1983 and commonly assigned U.S. Pat No. 4,747,991issued to Bishop on May 31, 1988, each of which are hereby incorporatedherein by reference, fully disclose how to construct tubular formingstructures which are capable of producing three-dimensionally expandedfilms which are uniformly debossed, but apertured only in predeterminedareas.

It is believed that the description contained herein will enable oneskilled in the art to practice the present invention in many and variedforms. Nonetheless, the following exemplary embodiments and analyticalmethods are set forth for the purpose of illustrating the beneficialelastic reliability of particularly preferred low stress relaxationelastomeric materials of the present invention.

TEST METHODS

A. TENSILE STRENGTH AND ELONGATION AT FAILURE

The properties determined by this method may correlate with thestretchability of the elastomeric film. These properties are relevant tothe choice of material suitable for use as the elastic component of anabsorbent article, particularly pull-on diapers, training pants,disposable diapers with fasteners, or other absorbent garments for adultuse, that is substantially stretched when being put on.

A commercial tensile tester from Instron Engineering Corp., Canton,Mass. or SINTECH-MTS Systems Corporation, Eden Prairie, Minn. may beused for this test. The films are cut into 1″ wide in MD (the machinedirection of the film) by 4″ long in CD (the cross direction which is ata 90° angle from MD) specimens. The instrument is interfaced with acomputer for controlling the test speed and other test parameters, andfor collecting, calculating and reporting the data. The tensilestress-strain properties of the film are determined according to ASTMMethod D882-83. These tensile properties are measured at roomtemperature (about 20° C.). The procedure is as follows:

(1) choose appropriate jaws and load cell for the test; the jaws shouldbe wide enough to fit the sample, typically 1″ wide jaws are used; theload cells is chosen so that the tensile response from the sample testedwill be between 25% and 75%. of the capacity of the load cells or theload range used, typically a 50 lb load cell is used;

(2) calibrate the instrument according to the manufacture'sinstructions;

(3) set the gauge length at 2″;

(4) place the sample in the flat surface of the jaws according to themanufacture's instructions;

(5) set the cross head speed at a constant speed of 20″/min;

(6) start the test and collect data simultaneously; and

(7) calculate and report tensile properties including elongation atbreak, and load at 100% and 200% elongation. The average result of threesamples is reported.

B. Two Cycle Hysteresis Test

The properties determined by this method may correlate with the forcesconsumer feels from the side panel, waist band, or other elasticcomponents when initially applying the product and how the product fitsafter it has been put on.

A commercial tensile tester from Instron Engineering Corp., Canton,Mass. or SINTECH-MTS Systems Corporation, Eden Prairie, Minn. may beused for this test. The films are cut into specimens 1″ wide in MD by 4″long in CD. The instrument is interfaced with a computer for controllingthe test speed and other test parameters, and for collecting,calculating and reporting the data. The two cycle hysteresis is measuredat room temperature. The procedure is as follows:

(1) choose appropriate jaws and load cell for the test; the jaws shouldbe wide enough to fit the sample, typically 1″ wide jaws are used; theload cells is chosen so that the response from the sample tested will bebetween 25% and 75% of the capacity of the load cells or the load rangeused, typically a 50 lb load cell is used;

(2) calibrate the instrument according to the manufacture'sinstructions;

(3) set the gauge length at 2″;

(4) place the sample in the flat surface of the jaws according to themanufacture's instructions;

(5) set the cross head speed at a constant speed of 20″/min;

(6) start the two cycle hysteresis test and collect data simultaneously,the two cycle hysteresis test has ee following steps:

a) go to 200% elongation at the constant rate of 20″/min;

b) hold position for 30 seconds;

c) go to 0% strain at the constant speed of 20″/min;

d) hold position for 60 seconds;

e) go to 50% elongation at the constant speed of 20″/min;

f) hold position for 30 seconds; and

g) go to 0% strain; and

(7) calculate and report properties including stress relaxation at 200%elongation, and percent set. The average result of three samples isreported.

C. Sustained Load Stress Relaxation Test

The properties determined by this method may correlate with the forcesconsumer feels from the side panel, waist band, or other elasticcomponents of the product and how the product fits at body temperatureafter it has been worn for a specified period of time. The propertiesdetermined by this method is relevant to the choice of materials thatresist relaxation under sustained load at body temperature(approximately 100° F.), hence provide sustained fit over the maximumwear time of an absorbent article.

A commercial tensile tester from Instron Engineering Corp., Canton,Mass. or SINTECH-MTS Systems Corporation, Eden Prairie, Minn. may beused for this test. The films are cut into specimens 1″ wide in MD by 2″long in CD. Mark 1″ gauge length on the sample and wrap tapes around thesample outside the gauge length marks to provide better surface forgripping by the jaws. The instrument is interfaced with a computer forcontrolling the test speed and other test parameters, and forcollecting, calculating and reporting the data. The sustained loadstress relaxation is measured at 100° F. (about human body temperature).The procedure is as follows:

(1) choose appropriate jaws and load cell for the test; the jaws shouldbe wide enough to fit the sample, typically 1″ wide jaws are used; theload cells is chosen so that the response from the sample tested will bebetween 25% and 75% of the capacity of the load cells or the load rangeused, typically a 50 lb load cell is used;

(2) calibrate the instrument according to the manufacture'sinstructions;

(3) set the gauge length at 1″;

(4) place the sample in the flat surface of the jaws according to themanufacture's instructions;

(5) set the cross head speed at a constant speed of 10″/min;

(6) start the sustained load stress relaxation test and collect datasimultaneously, the sustained load stress relaxation test has thefollowing steps:

a) go to 200% elongation at the constant rate of 10″/min;

b) hold position for 30 seconds;

c) go to 0% strain at the constant speed of 10″/min;

d) hold position for 60 seconds;

e) go to 50% elongation at the constant speed of 10″mm;

f) hold position for 10 hours; and

g) go to 0% strain; and

(7) calculate and report properties including initial and final load(i.e., the Final Sustained Load), and % loss. The average result ofthree samples is reported.

The % loss is the stress relaxation at sustained load at 10 hours and isexpressed as [(initial load at 50% elongation of cycle 2—final load at50% elongation of cycle 2 after 10 hours)/initial load at 50% elongationof cycle 2]×100.

EXAMPLES

Extrudable and formable elastomeric compositions are prepared byblending varying amount of a styrenic elastomeric copolymer such asKraton® G1600 series form Shell Chemical Company, Houston, Tex., orSEPTON® S4000 or S8000 series form Kuraray America, Inc., New York,N.Y., a vinylarene resin such as polystyrene PS210 from Nova Chemical,Inc. Monaca, Pa., and mineral oil such as Drakeol® available fromPennzoil Co., Penrenco Div., Karns City, Pa., to form an elastomericmixture.

Examples of the elastomeric composition suitable for use herein areshown in Table 1. The amount of each component is expressed in weightpercent of the elastomeric composition. Additives, specificallyantioxidants, which are present only in small amounts are not shown inthe compositions of TABLE 1. Typically, the elastomeric compositionsuseful in the present invention comprise about 0.5 wt % of antioxidants.

TABLE 1 Elastomeric Compositions (Weight Percent) Sample 1 2 3 4S-E-EP-S Block Copolymer 55 55 55 55 Septon ® S-4033 Polystyrene PS21015 10 10 Resin Piccotex ® 120 15  5 Resin Kristalex ® 5140  5 MineralOil Drakeol ® 30 30 30 30

The physical properties of extruded monolayer films of the elastomericcompositions of TABLE 1 are shown in TABLE 2 These properties aredetermined by the TEST Methods described hereinabove. All physicalproperties in Table 2 are expressed on an equal basis weight of the filmsamples. TABLE 2 illustrates that replacing polystyrene with lowermolecular weight aromatic hydrocarbon resins provides surprisinglyequivalent elastic and stress relaxation properties, even though thetotal weight percent of the composition constituting thethree-dimensional entangled network is reduced.

TABLE 2 Properties of The Extruded Films of The Elastomeric CompositionsSample 1 2 3 4 Basis Weight (g/m2) 70 70 70 70 Stress at 100% Elongation(g/in) 183 226 182 179 Stress at 200% Elongation (g/in) 267 261 252 266Stress Relaxation at 200% 6 11 7 7 Elongation (%) Set After A FirstCycle 1 3 2 1 to 200% Elongation (%) Final Sustained Load 86 68 74 82 at50% Elongation (g/in) Stress Relaxation at Sustained 27 43 35 28 Load at10 hours (%) % Elongation at Break 721 660 737 666

The physical properties of composition 1 disclosed in TABLE 3 aredetermined as an extruded monolayer elastomeric film, as a co-extrudedmultilayer film and as a three-dimensional vacuum formed web.

A planar coextruded multilayer film is produced and then formed bymethods disclosed above into an elastomeric web, generally as shown inthe photomicrographs of FIGS. 9-11. The coextruded film comprises threelayers as depicted in FIG. 4. The center elastomeric layer comprisesstyrenic triblock copolymer blended with polystyrene and mineral oil,and optionally aromatic hydrocarbon resins. The elastomeric layer istypically about 0.052 mm (3.2 mils) thick. The skin layers comprisepolyolefin materials and each is typically about 0.0038 mm (0.15 mil)thick. The total gauge of the film is approximately 0.09 mm (3.5 mils)with the elastomeric layer being approximately 75-90% of the thickness.A monolayer elastomeric film is also produced by methods generally knownin the art to form a film of about 0.072 mm (2.8 mils) thick. The filmsare cut to into proper sample size according to the test methodsdescribed hereinabove.

While being difficult to measure accurately, the gauge of thethree-dimensional elastomeric web from the first surface to the secondsurface was on the order of 1 mm, for a draw ratio of approximately10:1. In an as-formed, unextended configuration the continuous firstsurface generally formed a regular pattern of 1 mm squarefluid-permeable apertures spaced about 1 mm apart on all sides. Thesecondary apertures were slightly smaller than the primary aperturesgiving the elastomeric web an open apertured area of approximately12-16%.

The exemplary elastomeric web of the present invention exhibitedreliable elastic performance by repeated and sustained web strains of upto about 400% or more without significant affect on web elasticity orporosity. In general, the web exhibited a higher modulus in the firstextension as the skin layers experienced inelastic strain. Thereafter itis believed that microscopic rugosities formed on the interconnectingmembers in the regions of inelastic skin layer strain, which resulted ina lower and generally constant web modulus.

TABLE 3 Properties of The Elastomeric Films/Webs Sample 1a 1b 1c BasisWeight (g/m2) 71 89 88 Stress at 100% Elongation (g/in) 186 293 258Stress at 200% Elongation (g/in) 271 346 307 Stress Relaxation at 200% 611 13 Elongation (%) Set After A First Cycle 1 8 10 to 200% Elongation(%) Final Sustained Load 87 98 76 at 50% Elongation (g/in) StressRelaxation at Sustained 27 33 33 Load at 10 hours (%) % Elongation atBreak 721 667 669

wherein Sample 1a is an extruded monolayer elastomeric film ofcomposition 1; Sample 1b is a coextruded multilayer film havingcomposition 1 as the center layer and polyethylene as the skin layersdisposed on the opposed surfaces of the center layer; and sample 1c is athree-dimensional elastomeric web formed according to the methodsdescribed hereinabove from the multilayer coextruded film of 1b.

The disclosures of all patents, patent applications (and any patentswhich issue thereon, as well as any corresponding published foreignpatent applications), and publications mentioned throughout thisdescription are hereby incorporated by reference herein. It is expresslynot admitted, however, that any of the documents incorporated byreference herein teach or disclose the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A low stress relaxation elastomeric film suitablefor being formed into a porous, macroscopically-expanded,three-dimensional elastomeric web, said elastomeric material comprisingan elastomeric layer having opposed first and second surfaces and atleast one substantially less elastomeric skin layer substantiallycontinuously joined to said first surface of the elastomeric layer, saidelastomeric layer comprising: a) from about 20 to about 80 wt % of anelastomeric block copolymer, said copolymer comprising from about 10% toabout 80% by weight of at least one hard block and from about 20% toabout 90% by weight of at least two soft block; b) from about 3 to about60 wt % of at least one vinylarene resin; and c) from about 5 to about60 wt % of a processing oil; wherein the elastomeric film has a stressrelaxation of less than about 20 percent at 200% elongation at roomtemperature and a stress relaxation of less than about 45 percent afterabout 10 hours at 100° F. and 50% elongation.
 2. The film of claim 1wherein the elastomeric layer comprises from about 20% to about 95% ofthe total thickness of the film and the skin layer comprises from about1% to about 40% of the total thickness of the film.
 3. The film of claim1 wherein the elastomeric layer is from about 0.5 mil to about 20 milsthick and the skin layer is from about 0.05 mil to about 5 mils thick.4. The film of claim 1 wherein the elastomeric block copolymer isselected from the group consisting of A-B-A triblock copolymers, A-B-A-Btetrablock copolymers, A-B-A-B-A pentablock copolymers, and mixturesthereof, wherein A is a hard block and B is a soft block.
 5. The film ofclaim 4 wherein the elastomeric block copolymer comprises more than oneA block derived from different vinylarene monomers and more than one Bblock derived from different olefinic monomers.
 6. The film of claim 1wherein the hard block is a polymer derived from vinylarene monomersselected from the group consisting of styrenes, α-methyl styrenes, otherstyrene derivatives, and mixtures thereof, and the soft block is apolymer derived from olefinic monomers selected from the groupconsisting of ethylenes, propylenes, butylenes, isoprenes, butadienes,and mixtures thereof.
 7. The film of claim 6 wherein the hard block ispolystyrene and the soft block is a polymer selected from the groupconsisting of poly(ethylene/propylene), poly(ethylene/butylene),polyisoprene, polybutadiene, hydrogenated poly(isoprene/butadiene), andmixtures thereof.
 8. The film of claim 1 wherein the hard block is acopolymer derived form vinylarene monomers and olefinic monomers, andthe soft block is a polymer derived from olefinic monomers.
 9. The filmof claim 1 wherein number-average molecular weight of the hard blockranges from about 1,000 to about 200,000, and number-average molecularweight of the soft block ranges from about 1,000 to about 300,000. 10.The film of claim 1 wherein number-average molecular weight of the hardblock ranges from about 5,000 to about 60,000, and number-averagemolecular weight of the soft block ranges from about 20,000 to about100,000.
 11. The film of claim 1 wherein glass transition temperature ofthe vinylarene resin ranges from about 58° C. to about 180° C.
 12. Thefilm of claim 1 wherein the vinylarene resin is derived from monomersselected from the group consisting of styrenes, α-methyl styrenes, otherstyrene derivatives, vinyl toluenes, and mixtures thereof, and has anumber-average molecular weight in the range from about 600 to about200,000.
 13. The film of claim 12 wherein the vinylarene resin ispolystyrene having a number-average molecular weight in the range fromabout 5,000 to about 150,000.
 14. The film of claim 12 wherein thevinylarene resin is a mixture of a polystyrene and a low molecularweight aromatic hydrocarbon resin at a concentration ratio ofpolystyrene to low molecular weight aromatic hydrocarbon resin in therange of from about 1:10 to about 10:1, said polystyrene has anumber-average molecular weight of about 10,000 to about 100,000 andsaid aromatic hydrocarbon resin has a number-average molecular weight ofabout 600 to about 10,000.
 15. The film of claim 1 wherein theprocessing oil is a mineral oil.
 16. The film of claim 1 wherein theelastomeric layer further comprises up to about 1 wt % of anantioxidant.
 17. The film of claim 1 wherein the film comprises two skinlayers, each of said skin layer being substantially continuously joinedto one of said opposed surfaces of the elastomeric film.
 18. The film ofclaim 1 wherein the skin layer comprises a thermoplastic polymerselected from the group consisting of polyolefins, ethylene copolymers,polystyrenes, poly(α-methyl styrenes), styrenic random block copolymers,polyphenylene oxides, and mixtures thereof.
 19. The film of claim 18wherein the skin layer is a polyolefin derived from the monomersselected from the group consisting of ethylenes, propylenes, butylenes,isoprenes, butadienes, 1,3-pentadienes, α-alkenes, and mixtures thereof.20. The film of claim 1 further comprising a fibrous nonwoven materialbonded to at least one surface of the elastomeric film such that saidelastomeric film and said nonwoven material form a composite laminate.21. An article to be worn adjacent to a person's body, said articlecomprising an elasticized portion comprising a low stress relaxationelastomeric film comprising an elastomeric layer having opposed firstand second surfaces; and at least one substantially less elastomericskin layer substantially continuously joined to said first surface ofthe elastomeric layer, said elastomeric layer comprising: a) from about20 to about 80 wt % of an elastomeric block copolymer, said copolymercomprising from about 10% to about 80% by weight of a hard block derivedfrom vinylarene monomers selected from the group consisting of styrenes,α-methyl styrenes, other styrene derivatives, and mixtures thereof andfrom about 20% to about 90% by weight of a soft block derived fromolefinic monomers selected from the group consisting of ethylenes,propylenes, butylenes, isoprenes, butadienes, and mixtures thereof; b)from about 3 to about 60 wt % of at least one vinylarene resin having aglass transition temperature from about 58° C. to about 180° C.; and c)from about 5 to about 60 wt % of a processing oil; wherein theelastomeric film has a stress relaxation of less than about 20 percentat 200% elongation and room temperature and a stress relaxation of lessthan about 45 percent after about 10 hours at 100° F. and 50%elongation.
 22. The article of claim 21 wherein said elasticized portionis side panels, waist bands, cuffs, topsheets, backsheets, bandages,wraps, or wound dressings.
 23. The article of claim 21 is an absorbentarticle comprising a chassis, wherein said chassis comprises a liquidpervious topsheet, a liquid impervious backsheet joined to saidtopsheet, and an absorbent core disposed between at least a portion ofsaid topsheet and said backsheet.
 24. The article of claim 23, whereinsaid absorbent article is pull-on diapers, training pants, disposablediapers with fasteners, feminine napkins, pantiliners, or incontinencegarments.
 25. The article of claim 21 wherein number-average molecularweight of the hard block ranges from about 1,000 to about 200,000, andnumber-average molecular weight of the soft block ranges from about1,000 to about 300,000.
 26. The article of claim 21 whereinnumber-average molecular weight of the hard block ranges from about5,000 to about 60,000, and number-average molecular weight of the softblock ranges from about 20,000 to about 100,000.
 27. A low stressrelaxation elastomeric material suitable for being formed into a porous,macroscopically-expanded, three-dimensional elastomeric web, saidelastomeric material comprising: a) from about 20 to about 80 wt % of anelastomeric triblock copolymer comprising a polyolefin midblock and twopolystyrene endblocks, the copolymer is selected from the groupconsisting of poly(styrene-ethylene/butylene-styrene), hydrogenatedpoly(styrene-isoprene/butadiene-styrene),poly(styrene-isoprene-styrene), poly(styrene-butylene-styrene),poly(styrene-ethylene/propylene-styrene), and mixtures thereof; b) fromabout 3 to about 60 wt % of at least one vinylarene resin having a glasstransition temperature from about 58° C. to about 180° C.; and c) fromabout 5 to about 60 wt % of mineral oil.
 28. The material of claim 27wherein number-average molecular weight of the hard block ranges fromabout 1,000 to about 200,000, and number-average molecular weight of thesoft block ranges from about 1,000 to about 300,000.
 29. The material ofclaim 27 wherein the vinylarene resin is derived from monomers selectedfrom the group consisting of styrenes, α-methyl styrenes, other styrenederivatives, vinyl toluenes, and mixtures thereof, and has anumber-average molecular weight in the range from about 600 to about200,000.
 30. The material of claim 29 wherein the vinylarene resin ispolystyrene having a number-average molecular weight in the range fromabout 5,000 to about 150,000.
 31. The material of claim 27 wherein thevinylarene resin is a mixture of a polystyrene and a low molecularweight aromatic hydrocarbon resin at a concentration ratio ofpolystyrene to low molecular weight aromatic hydrocarbon resin in therange of from about 1:10 to about 10:1, said polystyrene has anumber-average molecular weight of about 10,000 to about 100,000 andsaid aromatic hydrocarbon resin has a number-average molecular weight ofabout 600 to about 10,000.
 32. The material of claim 27 wherein saidmaterial comprises an elasticized portion of an article to be wornadjacent to a person's body.
 33. The material of claim 32 wherein saidelasticized portion is side panels, waist bands, cuffs, topsheets,backsheets, bandages, wraps, or wound dressings.
 34. The material ofclaim 32 wherein said article is an absorbent article comprising achassis, said chassis comprises a liquid pervious topsheet, a liquidimpervious backsheet joined to said topsheet, and an absorbent coredisposed between at least a portion of said topsheet and said backsheet.35. The article of claim 34, wherein said absorbent article is pull-ondiapers, training pants, disposable diapers with fasteners, femininenapkins, pantiliners, or incontinence garments.